Cannabis Use During Pregnancy and Breastfeeding

Key Points

• Cannabis is the second-most common psychoactive substance (after

alcohol) used during pregnancy.

• Elements of cannabis can pass through the placenta and affect the fetus’s

development. Frequent cannabis use during pregnancy is associated

with low birth weight and is part of a cluster of risk factors related to other

adverse birth outcomes.

• There are also affects on behaviour in children and young adults, including

attention deﬁcits, emotional disturbances, increased hyperactivity and

impulsivity, sleep disorders, and increased likelihood of substance use.

• Growing evidence from human and animal studies shows that paternal

cannabis use can also negatively affect children’s neurodevelopment.

• Elements of cannabis can pass into breastmilk during lactation, which the

infant absorbs and metabolizes.

• The effects of cannabidiol (CBD) use during pregnancy or breastfeeding

are unknown. Both clinical and preclinical studies are urgently needed to

evaluate the safety of CBD use during pregnancy.

• Information on the effects of cannabis use during pregnancy is essential to

help healthcare providers advise patients about the effect of cannabis use

and improve the health and well-being of patients and their children.

• Pregnant or breastfeeding parents should have informed discussions with

healthcare providers about the potential adverse effects of cannabis use

during pregnancy to help them better understand the potential risks and help

them make informed and healthy choices.

Clearing the Smoke

on Cannabis

Cannabis Use During Pregnancy

and Breastfeeding

– An Update

Justine Renard, Ph.D.,

Research and Policy Analyst, CCSA

Sarah Konefal, Ph.D.,

Research and Policy Analyst, CCSA

This is the second in a series of

reports that reviews the effects of

cannabis use on various aspects of

human functioning and development.

This report focuses on maternal

cannabis use during pregnancy and

breastfeeding and its effects on

children and young adults. It updates

a previous report with new research

ﬁndings that validate and extend our

understanding of this issue. Other

reports in this series address the

effects on mental health, driving,

respiratory and cardiovascular health,

medical use, cognitive function and

edibles. This series is intended for

public health professionals, including

program managers and coordinators,

educators and health promoters,

prevention experts, direct healthcare

providers (e.g., physicians, nurses,

pharmacists), policy and decision

makers, and researchers.

Clearing the Smoke on Cannabis: Cannabis Use During Pregnancy and Breastfeeding

Background

After alcohol, cannabis (also referred

to as marijuana) is the most widely

used psychoactive substance in

Canada. According to the cross-

sectional National Cannabis Survey,

in 2020, 20.0% of Canadians aged

15 years and older reported using

cannabis in the previous three

months, and 7.9% reported daily

use, a signiﬁcant increase from 2018

(5.4%) and 2019 (6.1%) (Statistics

Canada, 2021). The use of cannabis

in 2020 was generally more prevalent

among young people (15–24years),

with 19.2% of youth aged 15 to

17years and 35.6% of young adults

aged 18 to 24 years reporting use in

the previous three months.

A growing body of evidence sug-

gests that cannabis use can nega-

tively affect several aspects of people’s lives, including men-

tal and physical health, cognitive functioning, ability to drive

a vehicle, and pre- and postnatal development among chil-

dren. One in a series reviewing the effects of cannabis use

on various aspects of human functioning and development

(Gabrys & Porath, 2019; Konefal et

al., 2019; Renard, 2020), this report

explores the effects of prenatal can-

nabis exposure on offspring, including

the birth outcomes, neurodevelop-

ment processes, behaviour and

mental health of children. Following

a review of the evidence, we discuss

implications for policy and practice.

Much of the available evidence on

this topic comes from three pro-

spective longitudinal cohort studies

and four retrospective cohort stud-

ies. The longitudinal studies describe

the effects of cannabis use during

pregnancy on child development and

behaviour. Table 1 summarizes these

studies’ details. The prospective longi-

tudinal nature of these studies follows

the same group of mothers and chil-

dren over a long period. This allows for

reliable measurement of the extent and timing of cannabis

exposure, as well as many lifestyle variables (e.g., maternal

health, socioeconomic status, maternal use of drugs other

than cannabis) during pregnancy and assesses the develop-

mental differences in children’s behaviour and functioning.

Table 1. Summary of details from three longitudinal, prospective cohort studies evaluating outcomes of maternal cannabis use during pregnancy

Variable

Ottawa Prenatal

Prospective Study (OPPS)

Maternal Health Practices

and Child Development

(MHPCD) Generation R

Reference Fried et al., 1984 Day et. al, 1992 El Marroun et al., 2009

Start year 1978 1982 2001

Location Ottawa, Canada Pittsburgh, USA Rotterdam, Netherlands

Sample demographic Caucasian, predominantly

middle-class families

Mostly black women from low

socioeconomic backgrounds

Multiethnic cohort with

predominantly higher

socioeconomic status

Total sample size 583 763 7,452

Initial sample size (cannabis

exposed

during pregnancy)

78 307 214

Categorization of cannabis

exposure

Irregular use (no more than

one marijuana cigarette per

week or 2nd hand smoke),

moderate use (average 2–5

per week) or heavy use

(average use greater than 5

per week)

Light use (between 0.0 and

0.4 average daily joints (ADJ),

moderate use (between 0.4

and 1 ADJ) or heavy use (1 or

more ADJ)

Occasional (monthly),

moderate (weekly), heavy

(daily) or no use

Times at which maternal

cannabis use measured

Rate of use calculated at each

trimester

Rate of use calculated at each

trimester, and at 8 months,

18 months and 36 months

postpartum

Rate of use calculated before

pregnancy, in early pregnancy

and in late pregnancy

Including women who also smoked tobacco and who may have only used cannabis during the ﬁrst trimester.

Cannabis, also called marijuana, refers

to products of the cannabis plant.

It is usually a greenish or brownish

material consisting of the dried

ﬂowering fruiting tops and leaves of

the cannabis plant. Cannabis contains

more than 100 cannabinoids,

with delta-9-tetrahydrocannabinol

(THC) being the main psychoactive

ingredient responsible for the high

that people feel. Cannabidiol (CBD)

is the second-most common

cannabinoid in cannabis. Cannabidiol

is not associated with the high and

is being studied for various medical

applications, such as relieving pain,

anxiety and other chronic conditions.

Clearing the Smoke on Cannabis: Cannabis Use During Pregnancy and Breastfeeding

The retrospective studies looked at past and archived data

to examine the potential risk factors (including cannabis

use) that could increase the risk for a disease. Those risks

were compared between participants who were exposed

and not exposed after the exposure and the outcome had

already occurred. Table 2 summarizes the four most rel-

evant retrospective cohort studies describing the effects of

cannabis use during pregnancy on child development and

behaviour. As these studies were conducted before Canada

legalized recreational cannabis occurred in October 2018,

the prevalence of cannabis use may have changed since

then. More data needs to be collected to examine the

effects of legalization on prenatal cannabis use.

Prevalence, Reasons and Perceptions of

Cannabis Use During Pregnancy

In Canada, about 47.6% of women of childbearing age

(i.e., 15–44 years) reported lifetime use of cannabis in 2017

(Statistics Canada, 2019). In 2020, 23% of women aged

16–19 years, 20% of women aged 20–24 years and 19%

of women aged 25 years and older reported daily or almost

daily cannabis use in the past year (Health Canada, 2021c).

Even more striking, in the northern territories of Canada

such as Nunavut, 70% of women aged 15–19 years and

50% of women aged between 25 and 44 years have used

cannabis in the past year (Reece & Hulse, 2020).

The Canadian Alcohol and Drugs Survey (CADS) showed

that in 2019, 5% of women of childbearing age reported

using cannabis during their last pregnancy, and 6% while

breastfeeding (Health Canada, 2021a). Data from the Better

Outcomes Registry & Network (BORN) database of live

and stillbirths in Ontario between April 2012 and December

2017 showed that the prevalence of cannabis use during

pregnancy increased by 61% from 1.2% in 2012 to 1.8%

in 2017 (Corsi, Hsu et al., 2019). Increases in the preva-

lence of cannabis use during pregnancy were predomin-

ately observed among younger women aged 15 to 24

years (5.49%) and those with lower socioeconomic status

(3.11%). Another recent study of 478 pregnant women in

the greater Hamilton area, Ontario, showed that 4.2% of

survey respondents reported using cannabis despite being

aware of potential risks of harm for the fetus (Bartlett et al.,

2020). Another recent survey from a women’s health unit

Table 2. Summary of details from four retrospective cohort studies evaluating outcomes of maternal cannabis use during pregnancy

Retrospective

Cohort Study

ABCD (Winiger &

Hewitt, 2020)

ABCD (Paul et al.,

2020)

BORN (Corsi, Walsh

et al., 2019)

BORN (Corsi et al.,

2020)

Collection of data June 1, 2016, to Oct.

15, 2018, from children

born between 2005

and 2009

June 1, 2016, to Oct.

15, 2018, from children

born between 2005

and 2009

Births and stillbirths

between April 2012

and December 2017

Births occurring

between April 1, 2007,

and March 31, 2012

Location 22 sites in the USA 22 sites in the USA Ontario Ontario

Sample size 11,875 11,489

Matched cohort

98,512 records

Matched cohort

173,035 records

Cannabis exposed 695 655 (413 were

exposed only before

maternal knowledge

of pregnancy, 235

both before and after

maternal knowledge,

and seven only after

maternal knowledge)

Matched group:

5,639 cannabis

exposed

Matched group:

2,364 cannabis

exposed

Cannabis exposure Self-reporting ever

using cannabis while

pregnant

Self-reporting using

cannabis either before

maternal knowledge of

pregnancy only, after

maternal knowledge

of pregnancy only

or before and after

maternal knowledge of

pregnancy

Self-reporting ever

using cannabis while

pregnant during

routine prenatal care

Self-reporting ever

using cannabis during

the ﬁrst prenatal

consultation (occurring

between 11 weeks

2days and 13 weeks

3day of gestation)

Note. ABCD = Adolescent Brain and Cognitive Development cross-sectional studies; BORN = Better Outcomes Registry & Network.

Only participants with no missing records of cannabis exposure during pregnancy were included in this study.

Matching strategy avoided critical potential confounders and ensured an equal distribution among exposed and nonexposed groups. In those

studies, cohort samples were matched for maternal obstetrical and sociodemographic characteristics between reported cannabis exposed and

nonexposed to reduce disparities in the sample.

Clearing the Smoke on Cannabis: Cannabis Use During Pregnancy and Breastfeeding

in Canada showed that 5% of preg-

nant women and 6.3% of breast-

feeding women were using cannabis

regularly (daily or weekly) (Manning

& Drover, 2020). A recent survey on

maternal health of 7,111 women in

Canada has shown that 3.1% of

respondents reported using can-

nabis during pregnancy and 2.6%

while breastfeeding (Grywacheski

et al., 2021). Sociodemographic

and mental health factors, including

lower level of education, thoughts of

self-harm, postpartum depression,

anxiety symptoms or any combina-

tion of these were associated with

cannabis use during pregnancy,

breastfeeding or both. Finally, a

study conducted in British Columbia

showed that maternal cannabis use

has increased over the past decade

from 2.2% in 2008 to 3.3% in 2016

(Luke et al., 2019). Younger age,

polysubstance use, lower socio-

economic status and history of men-

tal illness were factors associated

with cannabis use during pregnancy.

Overall, the prevalence of cannabis use during pregnancy

in several Canadian studies ranges from about 2% to 5%

(Badowski & Smith, 2020). However, because prevalence

measures largely rely on self-reporting, prevalence rates are

likely underestimated due to stigma or other fears (i.e., child

services intervention). For example, a study conducted in

Pittsburgh found that only 36% of pregnant patients who

tested positive for etrahydrocannabinol (THC) had disclosed

their cannabis use (Chang et al., 2017). An older study ana-

lyzing the effects of prenatal cannabis and alcohol exposure

on child academic performance at age 10 showed that 14%

of women were using cannabis regularly (i.e., smoking one

or more joints daily) during the ﬁrst trimester of pregnancy,

compared with 5.3% and 5.0% during second and third tri-

mesters, respectively (Goldschmidt et al., 2012). Prevalence

of cannabis use during pregnancy can be as high as 15% to

28% in disadvantaged, urban or low-income women (Beatty

et al., 2012; Passey et al., 2014; Schempf & Strobino, 2008).

Other recent studies have indicated that in the United States,

younger age (before 25 years), lower education level, lower

socioeconomic status (unemployment, lower income), being

non-Hispanic or African-American, earlier trimester of preg-

nancy, marital status (i.e., not married), poor mental health

(i.e., anxiety or depression) and con-

comitant use of tobacco, alcohol or

both were risk factors for cannabis use

among pregnant women (Bayrampour

et al., 2019; Corsi, Hsu, et al., 2019;

Odom et al., 2020).

In addition, with easier accessibility to

cannabis, more legal product choices

available and increasing social accept-

ance, the prevalence of cannabis use

may have increased since the legaliza-

tion of nonmedical cannabis in October

2018 in Canada. For example, canna-

bis use during pregnancy (conﬁrmed

by urine toxicology test) increased in

California after legalization from 6%

to 11% (Lee et al., 2020). Another

study showed that the prevalence of

cannabis use during pregnancy (con-

ﬁrmed by urine toxicology test) was

as high as 18% in Colorado, which

also legalized recreational cannabis

(Rodriguez et al., 2019). In Ontario,

Canada, a prospective longitudinal

cohort study examined the conse-

quences of nonmedical cannabis legalization a year follow-

ing legalization (Turna et al., 2021). It showed that cannabis

use decreased among adults who were using cannabis

before legalization and increased among adults who were

not using cannabis before legalization.

While the impact of legalization on cannabis use in Canada

is not well established and more data need to be collected,

the prevalence of cannabis use may have changed since

the studies conducted before legalization.

Reasons for Cannabis Use During

Pregnancy

Over the past years, there has been an increasing belief that

cannabis is harmless and can relieve some of the symp-

toms of pregnancy, such as morning sickness, nausea and

vomiting, anxiety, and sleep disorders. This belief can be

promoted by healthcare providers, the cannabis industry

and nonmedical employees at retail cannabis dispensaries

(Bayrampour et al., 2019; Dickson et al., 2018; Metz &

Borgelt, 2018). For example, 69% of pregnant women in

Colorado cannabis dispensaries were recommended can-

nabis to alleviate morning sickness (Dickson et al., 2018).

It is also common for pregnant women to seek information

about cannabis and pregnancy from family and friends, as

There are different ways to use

cannabis. Cannabis can be ingested

(edible cannabis, oils, drinks, pills),

inhaled (smoked or vaped) or applied

to the skin. The duration of cannabis’s

effects depends on how it is used.

When inhaled, cannabis intoxicating

effects start within a few seconds to

a few minutes and peak within 30

minutes. Effects can last up to six

hours and residual effects can last up

to 24 hours. When ingested, cannabis

intoxicating effects do not kick in for

about 30 minutes to two hours and

peak at about four hours. The effects

can last up to 12 hours after use and

residual effects can last up to 24

hours. This timing differs from smoking

or vaping cannabis, where the effects

start to be felt within a few seconds or

minutes and peak at about 30 minutes.

Clearing the Smoke on Cannabis: Cannabis Use During Pregnancy and Breastfeeding

well as the internet and social media. However, a great deal

of inaccurate information is circulating on untrusted online

sources about the potential positive effects of cannabis on

some of these pregnancy symptoms. As a consequence,

many pregnant women report using cannabis during preg-

nancy to alleviate morning sickness, pain and mood disor-

ders (Metz & Borgelt, 2018). In another survey conducted in

Colorado, 63% of women reported using cannabis during

pregnancy to alleviate anxiety and depression symptoms,

and 60% reported using it for pain relief (Committee on

Obstetric Practice, 2017). Similarly, in a Canadian women’s

health unit survey, among the 5% of pregnant women using

cannabis, relieving anxiety symptoms (33.3%), sleep dis-

turbances (22.2%) and nausea or vomiting (22.2%) were

the most common reasons reported for cannabis use

(Manning & Drover, 2020).

Despite these ﬁndings, there is no evidence showing

that cannabis use during pregnancy can alleviate these

symptoms. Further robust randomized controlled studies

examining the efﬁcacy of cannabis in alleviating symptoms

associated with pregnancy as well as its safety during preg-

nancy are still needed. Meanwhile, increasing awareness

about the potential risks of cannabis use during pregnancy

and breastfeeding remains essential.

Perceptions of Cannabis Use During

Pregnancy

Pregnant women who use cannabis generally perceive

cannabis as having low risks for the fetus, compared with

pregnant women who do not use cannabis (Weisbeck et

al., 2021). A survey of 306 women in the United States

showed that 35% of pregnant women were using canna-

bis. Among those, 34% were not willing to quit cannabis

use during their pregnancy. Three-quarters (75%) of preg-

nant women who were using cannabis were more likely to

perceive cannabis use as harmless, compared with preg-

nant women who quit cannabis use (Mark et al., 2017).

In the 2021 Canadian Cannabis Survey, 83% of those who

used cannabis did not agree that it was reasonable to use

cannabis while pregnant or breastfeeding, which was the

same as in 2020 (Health Canada, 2021b). That is com-

pared with 88% of those who did not use cannabis in the

previous 12 months, which was down slightly from 90%

in 2020. In addition, 95% of women aged 16 to 50 years

who had given birth in the previous ﬁve years reported not

having used cannabis once they knew they were pregnant,

which was unchanged from 2020. Finally, 92% of women

reported not having used cannabis while breastfeeding

their child, which was also unchanged.

Another recent survey from the greater Hamilton area in

Ontario showed that most of the women surveyed were aware

that cannabis can pass to the fetus through the placenta

(94.3%) or to the infant through breastmilk (91.2%) (Bartlett

et al., 2020). Both can have risks to the infant’s development.

However, despite this high proportion of aware women, 4.2%

of them were still using cannabis while pregnant.

In a recent Canadian women’s health unit survey, 22.6% of

respondents said they believed that cannabis use during

pregnancy and breastfeeding was harmless, while 30.4%

were unsure of the potential harm of cannabis use during

pregnancy and breastfeeding (Manning & Drover, 2020).

In the United States, a qualitative study examining attitudes

and beliefs about prenatal cannabis use showed that preg-

nant women who used cannabis during pregnancy had

conﬂicting attitudes about their cannabis use while pregnant

(Chang et al., 2019). They reported trying to reduce can-

nabis use during pregnancy because of the potential risks

for the developing baby. On the other hand, they perceived

cannabis as being safer than other substances, including

prescribed medications, because it is a natural plant.

Finally, an integrative review that analyzed women’s percep-

tion showed that women who use cannabis during preg-

nancy generally perceived cannabis use as harmless com-

pared with women who do not use cannabis (Bayrampour

et al., 2019). Most pregnant women reported a lack of

information or recommendations from and communication

with their healthcare providers about the health effects of

prenatal cannabis use. This reinforces the idea that canna-

bis use during pregnancy may be harmless or insigniﬁcant.

All these ﬁndings have implications for how healthcare pro-

viders discuss the use of cannabis with pregnant patients.

Informed discussions with healthcare providers about the

potential adverse effects of using cannabis during pregnancy

are needed to help women make informed and healthy

choices (Bayrampour et al., 2019). In addition, person-

centred, harm reduction and trauma-informed approaches

are needed during these discussions to help ensure informed

and nonjudgmental discussions and build a trusting relation-

ship between healthcare providers and pregnant patients.

Effects on Pregnancy, Fetal Development

and Birth Outcomes

Fetal Development and Neonatal Birth

Outcomes

After controlling for maternal tobacco, alcohol and illicit

drug use and various demographic covariates, there is

conﬂicting evidence of an association between cannabis

Clearing the Smoke on Cannabis: Cannabis Use During Pregnancy and Breastfeeding

use during pregnancy and an increased risk of pregnancy

complications, premature birth, small head circumfer-

ence, small length, stillbirth or major congenital abnormal-

ities (Gunn et al., 2016; Metz & Stickrath, 2015; National

Academies of Sciences, Engineering, and Medicine, 2017).

However, substantial evidence highlights an elevated risk

for low birth weight in infants from mothers who used can-

nabis during pregnancy (National Academies of Sciences,

Engineering, and Medicine, 2017). Further, while reports

on the effects of prenatal cannabis exposure are mixed,

heavy cannabis use is more strongly associated with cer-

tain adverse outcomes of pregnancy.

In the Generation R study, maternal cannabis use dur-

ing pregnancy was associated with reduced fetal growth

in mid and late pregnancy as well as a lower birth weight

(El Marroun et al., 2009). These associations were

independent of various lifestyle and socioeconomic factors.

The results from this study also suggested a dose–response

relationship such that heavier cannabis use during preg-

nancy was particularly associated with lower birth weight.

Findings from the Maternal Health Practices and Child

Development (MHPCD) study noted a small but signiﬁcant

negative relationship between cannabis use during the ﬁrst

trimester and length of the child at birth (Day et al., 1991).

In a study of a large cohort of Australian women presenting

for public prenatal care at a large hospital between 2000

and 2006, Hayatbakhsh et al. (2012) reported that use of

cannabis during pregnancy signiﬁcantly predicted negative

birth outcomes, including low birth weight, preterm birth,

small for gestational age and admission to the neonatal

intensive care unit. These effects were independent of

the mother’s sociodemographic characteristics, cigarette

smoking, alcohol consumption and use of illicit drugs.

In contrast, the Ottawa Prenatal Prospective Study (OPPS)

did not observe any differences in growth measures at birth

between infants born to women using cannabis and those

not using cannabis (Fried & O’Connell, 1987). Fried et al.

(1984) noted a statistically signiﬁcant reduction of about

one week in the gestational age of infants born to moth-

ers in the OPPS who used cannabis six or more times per

week compared with those who did not.

Two recent meta-analyses assessed neonatal health out-

comes following maternal cannabis exposure. The ﬁrst

included results from 24 studies that did not control for poly-

substance use and found that exposure to cannabis in utero

was associated with decreased birth weight and an increased

likelihood of admission to the neonatal intensive care unit

(Gunn et al., 2016). The second included results from 31

observational cohort or case-control studies where canna-

bis and other substance use had been recorded (Conner et

al., 2016). The authors noted a signiﬁcantly elevated risk of

low birth weight and premature birth in women who used

cannabis. That risk doubled when the frequency of cannabis

use was at least once per week. However, these associations

disappeared after adjusting for tobacco use.

Three retrospective cohort studies not included in these

meta-analyses adjusted for concurrent tobacco use and

reported mixed results on risks associated with prenatal

cannabis exposure (Chabarria et al., 2016; Ko et al., 2018;

Warshak et al., 2015). Chabarria et al. (2016) found that

while smoking only cannabis had no signiﬁcant effect on

any of the birth outcomes assessed, both cannabis and

tobacco were associated with an increased risk for low birth

weight, preterm birth and decreased head circumference.

Ko et al. (2018) only looked at mean infant birth weight and

gestational age. After controlling for relevant covariates,

such as cigarette smoking, they found no signiﬁcant dif-

ferences in infants from women who used cannabis during

pregnancy. Warshak etal. (2015) reported an increased risk

for admission to the neonatal intensive care unit and small

for gestational age but no effect on birth weight. Smoking

cannabis during pregnancy was also found to increase the

odds of having an infant with low birth weight by almost

three times, although authors did not adjust their analysis

for tobacco or alcohol use (Campbell et al., 2018)

The large Ontario retrospective cohort study using the birth

registry (BORN) examined the association between pre-

natal cannabis exposure and adverse maternal and peri-

natal outcomes (Corsi, Walsh, et al., 2019). Authors ana-

lyzed births and stillbirths among women aged 15 years

and older between April 2012 and December 2017. They

found that in women who reported cannabis use during

pregnancy (1.4%), cannabis exposure was signiﬁcantly

associated with increased frequency of small for gesta-

tional age, placental abruption, greater transfer to neonatal

intensive care and an abnormal ﬁve-minute Apgar score

less than four.

In another recent study, cannabis use during pregnancy

(among other substances use) was associated with an

increased risk of small for gestational age (47% increased),

preterm birth (27% increased) and intrapartum stillbirth

(184% increased) (Luke et al., 2019). However, caution

should be taken as the authors did not rule out the effects

that other substance use may have had on pregnancy

outcomes.

The ﬁve-minute Apgar test is performed ﬁve minutes after birth on the newborn by the healthcare provider to examine different parameters such as

breathing, skin color, heart rate, muscle tone and reﬂexes. The score indicates to the healthcare provider how the newborn is doing outside of the womb.

Clearing the Smoke on Cannabis: Cannabis Use During Pregnancy and Breastfeeding

Finally, a retrospective observational cohort study was

conducted using health records data from 3,435 women

who received prenatal care and a subsequent singleton

live birth in Minnesota. Among those women, 283 (8.2%)

tested positive for THC via urine toxicology assays. Authors

showed that exposure to cannabis during pregnancy was

associated with small for gestational age and increased

abnormal 12-month developmental screens (Kharbanda et

al., 2020). Similarly, increased risk of small for gestational

age was shown in another recent study in which prenatal

THC exposure was also conﬁrmed using urine analyses

(Rodriguez et al., 2019).

In these studies, the authors concluded that the discrep-

ancy in other ﬁndings evaluating the effects of prenatal

exposure may be due to the uncertainty or underestima-

tion of prenatal cannabis use. In support of this idea, a

recent study showed that self-reported cannabis use dur-

ing pregnancy (conﬁrmed by urine toxicology testing) was

associated with adverse outcomes, including preterm birth,

hypertensive disorders of pregnancy,

stillbirth or small for gestational age

(Rodriguez et al., 2019). Importantly,

the odds of adverse outcomes were

higher in women who had more than

one positive THC urine test com-

pared with women who had negative

THC tests. Using THC urine analyses

to better conﬁrm the use of cannabis

during pregnancy would help to bet-

ter estimate the effects of cannabis

use during pregnancy.

Despite difﬁculties determining the

unique effects of cannabis exposure

on pregnancy and fetal development,

the National Academies of Sciences,

Engineering, and Medicine (2017)

report concluded that there was sub-

stantial evidence for a statistically sig-

niﬁcant association between maternal cannabis smoking

and low birth weight of infants exposed in utero. Low birth

weights were subsequently associated with poor long-term

outcomes throughout childhood and adulthood, including

increased risk for Type 2 diabetes, hypertension, cardio-

vascular disease and respiratory problems (Gluckman

etal., 2008; Statistics Canada, 2016).

However, it is yet unknown whether smoking as a means

of use can have negative effects rather than cannabis itself.

Cannabis smoking has been and still is the most common

method of cannabis use. Therefore, some of the negative

outcomes for infants of mothers using cannabis may be in

part related to other toxic chemicals inhaled when smoking.

To date, there have been no studies that have examined if

different methods of cannabis use (smoking, vaping, sub-

lingual or ingested) have different effects on fetal outcomes.

Further studies are needed to explore this question.

Congenital Abnormalities

Only a few correlational studies have demonstrated a link

between congenital abnormalities and prenatal cannabis

use. For instance, after adjusting for socioeconomic vari-

ables and the use of other substances such as tobacco

and opioids, a recent study analyzing health record data

in Canada found a positive correlation between rates of

cannabis use and rates of congenital anomalies in the terri-

tories (Reece & Hulse, 2020). This included cardiovascular

defects, orofacial clefts, Down syndrome and gastroschisis

(a defect in an infant’s abdominal wall). However, this ﬁnd-

ing should be treated with caution as this is a geospatial

paper and many confounding factors were not considered.

Other studies have also shown poten-

tial associations between prenatal

cannabis use and congenital anom-

alies, such as ventricular septal defects

(Williams et al., 2004), bowel matting

(Weinsheimer et al., 2008), gastro-

schisis, anencephaly and esophageal

atresia (van Gelder et al., 2014).

Findings from the above-mentioned

studies should be interpreted with

caution because a “positive correla-

tion” does not mean a “causal asso-

ciation” between prenatal cannabis

use and offspring congenital anom-

alies. Confounding factors may have

a role in this relationship, which may

establish causality between prenatal

cannabis exposure and congenital

anomalies. Most of the available studies examining this rela-

tionship, including the prospective longitudinal birth cohorts,

have not found an association between prenatal cannabis

use and increased risk for congenital anomalies in children

(Kharbanda et al., 2020).

Effects on Neurocognitive Functioning

and Neurodevelopmental Processes

Neurocognitive Functioning

Findings from the OPPS and MHPCD longitudinal stud-

ies suggest that maternal cannabis use during pregnancy

Regular and Heavy Cannabis Use

There is no single deﬁnition in the

scientiﬁc literature of what constitutes

regular cannabis use. The phrase

generally refers to weekly or more

frequent use over months or years

and poses a risk for adverse health

effects. Terms that are often used

interchangeably with regular use

include frequent use, chronic use and

long-term use. By contrast, heavy use

typically refers to daily or more frequent

use and can be a sign of dependence

and cannabis use disorder.

Clearing the Smoke on Cannabis: Cannabis Use During Pregnancy and Breastfeeding

18 months 3–6 years 9–11 years 14–16 years

17–22 years

Increased aggressive

behaviour

Attention deﬁcits

(females)

Deﬁcits in verbal and

perceptual skills,

a,b

verbal, quantitative

and visual reasoning,

a,b

short-term memory,

a,b

attention

a,b

and

vigilance

Hyperactivity

a,b

Impulsivity

a,b

Deﬁcits in abstract

and visual reasoning,

a,b

attention,

b,d

executive

functioning,

a,b

reading,

a,b

spelling,

a,b

attention,

b,d

and internalizing,

externalizing, and social

behaviours

Hyperactivity

a,b

Impulsivity

Depressive and anxious

symptoms

Psychotic-like

experiences

Thoughts disturbances

Long-term sleep

disorders

Deﬁcits in visual-

cognitive functioning,

academic

achievement,

information processing

speed

and visual-

motor co-ordination

Delinquency

Deﬁcits in executive

functioning,

response

inhibition

and

visuospatial working

memory

Smoking

a,b

Substance use

a,b

Early initiation of

substance use

a,b

Ottawa Prenatal Prospective Study (Fried et al., 1984)

Maternal Health Practices and Child Development (Day et al., 1992)

Generation R (El Marroun et al., 2009)

Adolescent Brain and Cognitive Development (Paul et al., 2021)

Adolescent Brain and Cognitive Development (Winiger & Hewitt, 2020)

Figure 1. Neurocognitive and Behavioural Effects

affects children’s neurocognitive development. Beginning at

age three to four years, children of mothers who used can-

nabis heavily while pregnant have shown deﬁcits in mem-

ory, verbal and perceptual skills, and verbal and visual rea-

soning after adjusting for potentially confounding variables

(Day etal., 1994; Fried & Watkinson, 1990). In contrast, the

results from the Generation R study did not ﬁnd evidence of

such cannabis-related deﬁcits when children were assessed

at about three years old (El Marroun, 2010). Impaired verbal

and quantitative reasoning and short-term memory have

also been found in the MHPCD among six-year-old chil-

dren whose mothers reported smoking one or more can-

nabis cigarettes per day while pregnant (Goldschmidt et al.,

2008). Both the OPPS and MHPCD studies reported that in

children about nine years of age, prenatal cannabis expos-

ure was linked with impaired abstract and visual reasoning,

poor executive functioning (i.e., visual-motor integration,

nonverbal concept formation and problem-solving) and

deﬁcits in reading, spelling and academic achievement

(Fried et al., 1998; Fried & Watkinson, 2000; Goldschmidt

et al., 2004; Richardson et al., 2002). Vulnerability in visual-

cognitive functioning has been shown to persist into early

adolescence among those children heavily exposed to

cannabis in utero (Fried et al., 2003).

Prenatal exposure to heavy maternal cannabis use during

the ﬁrst trimester also predicted signiﬁcantly poorer scores

on academic achievement tests (particularly in reading) at

the age of 14 years in the MHPCD (Goldschmidt et al.,

2012). Interestingly, these latter effects were found to be

related to prenatal cannabis exposure on intelligence test

performance at age six years, attention problems and

In all three longitudinal studies, the analyses controlled for various covariates such as the children’s gender and ethnicity, home environment,

maternal socioeconomic status, prenatal exposure to tobacco and alcohol, and current maternal substance use.

Clearing the Smoke on Cannabis: Cannabis Use During Pregnancy and Breastfeeding

depression symptoms at age 10 years and early start of

cannabis use. At the age of 16 years, deﬁcits in informa-

tion processing speed, interhemispheric transfer of infor-

mation and visual-motor coordination have been linked

with prenatal exposure to cannabis (Willford et al., 2010)

These effects were found with light to moderate prenatal

cannabis exposure in the MHPCD. However, general intelli-

gence does not appear to be affected by prenatal cannabis

exposure (Fried et al., 1998; Fried et al., 2003).

Findings from brain imaging studies of young adults aged

18–22 years enrolled in the OPPS showed that in utero

cannabis exposure negatively affects the neural circuitry

involved in aspects of executive functioning, including

response inhibition, attention and visuospatial working

memory (Smith et al., 2004; Smith et al., 2006; Smith et

al., 2016). Consistent with these ﬁndings, results from a

neuroimaging study with the Generation R cohort showed

altered brain morphology, speciﬁcally in the frontal cortex,

in children aged 6–8 years who were exposed prenatally

to cannabis (El Marroun etal., 2016). These ﬁndings are

also consistent with a report of altered functional connec-

tivity in neonates with prenatal cannabis exposure and

are particularly noteworthy as they show that smoking

cannabis during pregnancy can lead to long-term chan-

ges in children’s neurocognitive development (Grewen

et al., 2015).

In all three longitudinal studies mentioned above, the analy-

ses controlled for various covariates, such as the children’s

gender and ethnicity, home environment, maternal socio-

economic status, prenatal exposure to tobacco and alco-

hol, and current maternal substance use.

Finally, the longitudinal Adolescent Brain and Cognitive

Development (ABCD) study recruited children ages 9 to 11

years across the United States (Paul et al., 2021). Children

in this study will be followed until age 20 years and will

help characterize normal adolescent brain development

and factors that can affect neurodevelopment. One of the

ABCD cross-sectional studies examined whether prenatal

cannabis exposure in 655 children exposed to cannabis

prenatally before and after being aware of the pregnancy

can be associated with psychopathology symptoms in

middle childhood, such as psychotic-like experiences,

internalizing or externalizing problems, attention deﬁcits,

thought disturbances and social behaviour problems (Paul

et al., 2021). Cognition, sleep, birth weight, gestational age

at birth, body mass index and brain structure (i.e., total

intracranial volume, white matter volume and grey matter

volume) were also analyzed. The researchers accounted

for multiple confounding factors that were included in the

ABCD cross-sectional studies. They included ethnicity (e.g.,

White, Black, Asian, Indigenous, Paciﬁc Islander, Hispanic

and other), ﬁrst-degree familial history of psychopathology

(e.g., depression, psychosis, anxiety, mania and antisocial

behaviour), marital status, prenatal exposure to tobacco or

alcohol, unplanned pregnancy, prenatal vitamin, alcohol or

tobacco use, child sex, twin or multiple pregnancy, house-

hold income, birth weight, maternal age at birth, gestational

age when pregnancy was discovered, child age and moth-

er’s education. Findings from this ABCD cross-sectional

study showed that prenatal cannabis exposure after being

aware of the pregnancy was associated with greater dis-

turbances in attention, thought and social behaviours (Paul

et al., 2021).

Conversely, a recent critical review of data from 45 longi-

tudinal studies, including data from OPPS and MHPCD

cohorts, investigated the effects of prenatal cannabis

exposure on cognitive functioning in individuals aged

from 0 to 22 years (Torres et al., 2020). The authors

concluded that there were relatively few cognitive deﬁ-

cits observed in children who were prenatally exposed

to cannabis. According to the authors, most studies that

have shown cognitive deﬁcits did not compare measures

against a normative database that would have conﬁrmed

that ﬁndings were statistically signiﬁcant. Normative data

help characterize what is “normal” in a large, random and

representative population at a speciﬁc period and include

important other factors, such as age and education,

for example.

Neurodevelopmental Outcomes

A large Canadian retrospective cohort study using the

birth registry (BORN) from Ontario, analyzed the relation-

ship between cannabis use during pregnancy and neuro-

developmental outcomes in childhood (Corsi et al., 2020).

The authors analyzed births occurring between April 1,

2007, and March 31, 2012. Their ﬁndings showed that

prenatally cannabis exposed children had a 50% increased

risk for an autism diagnosis even after controlling for con-

founding factors, such as income, preterm birth and the

use of other substances (Corsi et al., 2020). However,

these ﬁndings should be taken with caution as other resid-

ual confounding factors, such as genetic vulnerabilities,

environmental factors, fetal and postnatal environment,

and dose and type of cannabis used, might still play a

role in this relationship, which ascertain causality between

prenatal cannabis exposure and the onset of later child-

hood neurodevelopmental disorders (Corsi et al., 2020).

The authors also pinpointed a small increased risk (11% to

22%) for developing intellectual deﬁcits, learning disorders

Clearing the Smoke on Cannabis: Cannabis Use During Pregnancy and Breastfeeding

and ADHD in prenatally cannabis exposed children com-

pared with nonprenatally exposed children. However, these

associations were no longer observed after controlling for

confounding factors (Corsi et al., 2020).

Behavioural Effects

Behavioural and Emotional Functioning

Outcomes

The behavioural effects of prenatal cannabis exposure have

also been documented, although it is unclear as to how

early such effects ﬁrst present themselves. The Generation

R study has reported that prenatal exposure to cannabis

is associated with an increased risk of aggressive behav-

iour and attention problems as early as 18 months of age

in girls, but not boys (El Marroun et al., 2011). At the age

of four years, the OPPS failed to ﬁnd evidence of a nega-

tive relationship between cannabis exposure and attention

(Fried & Watkinson, 1990), whereas the MHPCD found

impaired vigilance among exposed children at this age

(Noland et al., 2005). When children reached age six years,

the effects of maternal cannabis use during pregnancy

become much more evident. Children who were prenatally

exposed to cannabis— particularly those who were heavily

exposed — were found to be more hyperactive, inatten-

tive and impulsive compared with children who were not

exposed prenatally to cannabis (Fried et al., 1992; Leech

et al., 1999). At age 10 years, prenatally exposed children

display increased hyperactivity, inattention and impulsivity,

and show increased rates of delinquency and externaliz-

ing problems as reported by their mothers and teachers,

compared with children who were not exposed prenatally

to cannabis (Fried et al., 1998; Goldschmidt et al., 2000;

Richardson et al., 2002). The MHPCD reported that chil-

dren who were heavily exposed to cannabis during the

ﬁrst trimester (i.e., one or more joints per day) were almost

twice as likely to display delinquent behaviour at the age

of 14 years as the children who were not exposed to can-

nabis or those who were exposed to lesser amounts (Day

et al., 2011). The authors also noted that the relationship

between prenatal exposure to cannabis and delinquent

behaviour appeared to be mediated by the effects of can-

nabis on depressive symptoms and by attention deﬁcits in

children exposed to cannabis. However, in children ages

13–16 years, the effects of prenatal cannabis exposure

on some aspects of attention (i.e., ﬂexibility, encoding and

focusing) appeared to wane (Fried et al., 2003).

Similarly, another study assessed the potential causal asso-

ciation between prenatal cannabis exposure and behav-

ioural or emotional functioning in Dutch children aged seven

to 10 years (El Marroun et al., 2019). Findings showed that

maternal cannabis use during pregnancy was associated

with child externalizing behaviour problems, including harm-

ful, aggressive or antisocial behaviours directed at others

such as physical or relational aggression, delinquency,

bullying, deﬁance and vandalism. However, both maternal

cannabis use before pregnancy and paternal cannabis use

were also associated with externalizing problems in children.

This suggests that the association between prenatal can-

nabis exposure and behavioural or emotional functioning

problems observed in children was not caused by direct

in utero cannabis effects on fetal development but rather

through residual confounding variables, such as shared

genetic vulnerabilities, environmental factors, other variables

such as parental behaviours, or any combination of these

(El Marroun et al., 2019).

Consistent with this idea, a study showed that both pre-

natal tobacco and cannabis exposure were indirectly asso-

ciated with child externalizing problems at 16 months of

age, an effect potentially due to “harsh” parenting during

caregiver–child interactions (Schuetze et al., 2019). These

ﬁndings support other studies showing that regulation and

externalizing behaviour problems in children may be asso-

ciated with “harsh” parental behaviours, such as insensitiv-

ity, anger or hostility (Bradley & Corwyn, 2007; Gartstein

et al., 2013; Kochanska & Knaack, 2003; Velders et al.,

2011), behaviours that can be associated with cannabis

use (Ansell et al., 2015). Therefore, these data suggest

that beyond the potential direct effects of cannabis on fetal

development, regular use of cannabis by one or both par-

ents and associated parenting behaviours can also contrib-

ute to transgenerational behavioural or emotional problems.

Sleep Patterns

The long-term effects of prenatal cannabis exposure

on child sleep patterns were analyzed in another ABCD

cross-sectional study (Winiger & Hewitt, 2020). After con-

trolling for various confounding variables, the authors found

that maternal prenatal cannabis exposure was associated

with long-term sleep disorders, such as difﬁculty initiating

and maintaining sleep, arousal disorders, irregular sleep–

wake disorders and excessive drowsiness in children aged

9–10 years (Winiger & Hewitt, 2020).

These ﬁndings were consistent with another older study

showing that prenatal maternal cannabis exposure was

associated with long-term nocturnal sleep disturbances in

children aged three years (Dahl et al., 1995), suggesting

that in utero exposure to cannabis may have long-term

negative effects on children’s circadian regulation. Again,

other residual confounding variables, such as shared

genetic vulnerabilities, environmental factors or other

Clearing the Smoke on Cannabis: Cannabis Use During Pregnancy and Breastfeeding

variables, such as parental behaviours, can also play a

role in this relationship.

Substance Use

There is also accumulating evidence that shows prenatal

cannabis exposure may contribute to the start and fre-

quency of substance use during adolescence. Animal

studies showed that repeated exposure to THC in early

development may enhance responses to other addict-

ive substances later in life (Cadoni et al., 2001; Panlilio

etal., 2013). Porath and Fried (2005) reported that 16- to

21-year-old children (particularly males) of women who

used cannabis during pregnancy were at increased risk,

in a dose-related manner, for starting and the daily use of

tobacco and cannabis, compared with children of mothers

who did not use cannabis during pregnancy. Similar results

were noted by Day et al. (2006). At age 14 years, children of

mothers who used cannabis heavily while pregnant not only

reported using this substance more frequently than children

of women who did not use it, but they also started using

it at an earlier age. These ﬁndings were also evident when

the offspring were 22 years of age (Sonon et al., 2015).

The likelihood of cannabis use was related to the extent of

prenatal exposure.

The long-term behavioural effects of maternal cannabis

exposure may be particularly relevant in populations where

other socioeconomic risk factors are also present. The

continued use of cannabis by one or both parents in addi-

tion to parental attitudes toward cannabis can contribute to

transgenerational trends in substance use.

Effects on Children’s Mental Health

Depressive and Anxious Symptoms

Some evidence shows that in utero cannabis exposure can

be associated with symptoms of depression and anxiety.

After controlling for other drug use during pregnancy and

risk factors for childhood depression, children of women

using cannabis during pregnancy had signiﬁcantly more

depressive and anxious symptoms at age 10 years com-

pared with children of women who did not use cannabis

during pregnancy (Gray et al., 2005; Leech et al., 2006).

However, genetic and epigenetic mechanisms

can also

contribute to an increased risk of psychiatric disorders,

including anxiety and depression. For example, abnormal-

ities in dopaminergic activity have been shown in humans

exposed to cannabis in utero. The effect is believed to be

mediated through epigenetic mechanisms in brain areas

involved in anxiety and depression, such as the amyg-

dala, nucleus accumbens and ventral striatum (DiNieri

et al., 2011; Wang et al., 2004). Dopaminergic activity

abnormalities are important neurobiological markers of

psychiatric diseases, such as schizophrenia, anxiety and

depression disorders.

A recent study has shown that maternal cannabis use was

associated with increased anxiety, aggression and hyper-

activity in early childhood (i.e., ages 3 to 6 years) as well as

with the stress hormone, cortisol (Rompala et al., 2021).

This behavioural phenotype was associated with decreased

placental expression of important genes involved in immune

function, including proinﬂammatory cytokines and immune

cell–type markers. More studies are needed to better

understand the relationships between maternal cannabis

use, immune function and anxiety phenotype in children.

Psychotic Symptoms

There is also some evidence that shows that prenatal can-

nabis exposure is associated with psychotic symptoms.

For instance, data from the MHPCD study showed that

young adults who were exposed prenatally to cannabis

were 1.3 times more likely to display psychotic symptoms

compared with unexposed young adults after controlling

for other signiﬁcant covariates (Day et al., 2015).

Consistent with these ﬁndings, a recent prospective

cohort study analyzing data from the Generation R cohort

examined the potential link between parental (maternal

and paternal) cannabis use during pregnancy and the

onset of childhood psychotic symptoms (Bolhuis et al.,

2018). They found that both maternal and paternal can-

nabis use were associated with greater psychotic-like

symptoms in children aged 10 years. They suggested

the existence of other etiologic factors, such as genetics,

environment or familial behaviours, rather than direct in

utero mechanisms that may be involved in the relation-

ship between parental cannabis use and the onset of

psychotic experiences in children.

More recently, ﬁndings from the ABCD cross-sectional

study showed that prenatal cannabis exposure after being

aware of pregnancy was associated with greater psycho-

pathology symptoms at ages nine to 11 years even after

accounting for potentially confounding variables (Paul et

al., 2021). The authors suggested that prenatal canna-

bis exposure may be associated with an increased risk of

psychopathological symptoms, including psychotic-like

experiences, and cognitive and social disturbances, in

Epigenetic modiﬁcationsare alterations in the expression of a gene and involve complex molecular mechanisms, such as DNA methylation and histone

modiﬁcation. Environmental factors, such as diet, stress, pollution, toxicants, substance use and inﬂammation, can play important roles in epigenetic

modiﬁcations. Epigenetic modiﬁcations can lead to diseases, including cancers, autoimmune disorders, psychiatric diseases and diabetes.

Clearing the Smoke on Cannabis: Cannabis Use During Pregnancy and Breastfeeding

middle childhood and concluded

that pregnant women should avoid

using cannabis.

The potential impact of prenatal

cannabis exposure on the mental

health of children is critical to their

long-term health and well-being and

needs to be examined more care-

fully in further longitudinal studies.

Breastfeeding

Breastfeeding provides many health

beneﬁts to the development of an

infant, but these beneﬁts must be

weighed against any potential risks

resulting from exposure to can-

nabis during lactation. Concerns

about the use of cannabis during

lactation stem from observations

in humans showing that THC is

secreted in breastmilk (de Oliveira

Silveira et al., 2017; Garry et al.,

2009; Marchei et al., 2011; Merritt

et al., 2016; Metz & Stickrath, 2015)

and is also absorbed, metabolized

and excreted by the infant (Djulus et

al., 2005; Garry et al., 2009; Liston,

1998; Perez-Reyes & Wall, 1982).

In addition to THC, cannabidiol

(CBD) can also be found and can

accumulate in breastmilk after

maternal cannabis inhalation or

edible ingestion (Moss et al., 2021).

This is because cannabinoids are

highly lipophilic compounds and

can be stored in breastmilk, which

is a rich source of healthy fats.

Cannabinoid levels found in breastmilk mostly depend on

the dose and frequency of maternal cannabis use.

One study estimated that within four hours after a single

inhalation of cannabis, breastfed infants ingest about 2.5%

(range from 0.4% to 8.7%) of the maternal dose of THC

(Baker et al., 2018). Another older analysis calculated an

infant’s exposure to THC through ingestion in one feeding

to be 0.8% of the mother’s consumption (Bennett, 1996).

Other studies have shown that THC levels can stay in

breastmilk from six days to six weeks following maternal

cannabis use, with a THC half-life estimation of 20 days

(Bertrand et al., 2018; Cannabis, 2021). A prospective,

observational pharmacokinetic

study estimated the amount and

duration of THC levels in breast-

milk of 25 women who used can-

nabis while pregnant and gave birth

between Nov.1, 2016, and June 30,

2019 (Wymore et al., 2021). Data

showed that, among seven women

who self-reported abstinence from

cannabis (which was conﬁrmed

by plasma analysis), the estimated

half-life of THC in breastmilk was

17 days, with an estimated elimin-

ation time greater than six weeks.

Therefore, the idea of “pumping

and dumping” breastmilk right after

maternal cannabis use to reduce

infant cannabis exposure during

breastfeeding does not seem to be

relevant.

The effects of maternal canna-

bis exposure on infants through

breastmilk are not well studied. The

potential long-term effects of such

exposure on an infant’s developing

brain are still poorly documented

and any conclusions are generally

confounded by in utero cannabis

exposure. Several reports suggest

that the use of cannabis during

breastfeeding contributes to nega-

tive short-term effects on infants,

including sedation, lethargy and

poor feeding habits (Djulus et al.,

2005; Liston, 1998; Miller, 2012).

Two limited studies with very small

sample sizes have attempted to

examine the isolated effects of can-

nabis exposure through breastmilk on long-term infant

health and development. The ﬁrst study reported that

occasional use of cannabis during lactation did not affect

motor and mental development after one year (Tennes et

al., 1985). The second study suggested THC exposure

through breastmilk in the ﬁrst month after birth could be

associated with decreased motor development at age one

year (Astley & Little, 1990). Neither study adequately con-

trolled for prenatal exposure to THC.

Finally, breastfeeding encourages maternal behaviour and

bonding between the mother and infant. Maternal consump-

tion of cannabis can compromise mother–infant bonding,

What is the endocannabinoid

system?

The brain produces its own natural

compounds, called endocannabinoids,

which act like THC. Endocannabinoids,

which include anandamide (AEA) and

2-arachidonoylglycerol (2-AG), bind to

cannabinoid (CB1 and CB2) receptors.

Cannabinoid receptors are throughout

the brain and body, meaning that

cannabinoids can inﬂuence a broad

range of psychological and biological

processes, such as cognition, emotional

processing and regulation, stress

response, appetite, immune functioning,

the endocrine (hormone) system, sleep

and pain signalling (Zou & Kumar, 2018).

CB1 receptors are more concentrated

in the brain. THC can mimic the activity

of AEA and bind to the CB1 receptors to

exert its psychoactive effects. However,

THC binds CB1 receptors at much

higher levels than AEA, ﬂooding the

endocannabinoid system, leading to

altered functioning of each process.

This ﬂooding means that chronic use of

cannabis (i.e., repeated brain exposure

to THC) can alter the functioning of the

endocannabinoid system, which can

include changes in AEA and 2-AG activity,

and the distribution of cannabinoid

receptors (Jacobson et al., 2019).

Clearing the Smoke on Cannabis: Cannabis Use During Pregnancy and Breastfeeding

which may contribute to children’s neurodevelopmental alter-

ations later in life (Best Start Resource Centre, 2017; Shieh

& Kravitz, 2006). For example, recent studies have shown

that postnatal maternal cannabis use was associated with a

shorter breastfeeding duration compared with women who

did not use cannabis postpartum (Crume et al., 2018; Ko

etal., 2018). In addition, because cannabis affects alertness,

understanding and judgment, its use can also comprom-

ise parent–infant interactions (Best Start Resource Centre,

2017; Centre of Excellence for Women’s Health, 2017; Sachs

et al., 2013).

Breastfeeding mothers should also consider harms asso-

ciated with second-hand cannabis smoke, which is espe-

cially harmful for infants and young children (Best Start

Resource Centre, 2017; Centre of Excellence for Women’s

Health, 2017; Colorado Department of Public Health and

Environment, 2017; Wilson et al., 2017). Even though data

on the effects of second-hand cannabis smoke are still

emerging, experts recommend pregnant and breastfeeding

women avoid cannabis smoke as it contains many of the

same harmful chemicals as tobacco smoke, which has the

potential to harm a developing baby (Public Health Agency

of Canada, 2018).

In the absence of sufﬁcient evidence for an association

between cannabis use during lactation and health out-

comes for the infant, using cannabis during lactation is dis-

couraged due to potential risks (Committee on Obstetric

Practice, 2017; Reece-Stremtan & Marinelli, 2015; Society

of Obstetricians and Gynaecologists of Canada, 2022).

Further research is needed to fully evaluate the inﬂuence

of cannabis on maternal behaviour and the impact of this

inﬂuence on child development and outcomes. In addi-

tion, if women choose to continue using cannabis during

pregnancy, harm reduction strategies such as encouraging

them to use methods of cannabis consumption other than

smoking would be beneﬁcial.

Mechanisms of Action

In the human fetal brain, endogenous cannabinoid CB1

receptors (CB1Rs) are found as early as 14 weeks of gesta-

tion (Biegon & Kerman, 2001), with drastic changes occur-

ring in their expression throughout the gestational period in

different brain areas, notably the limbic structures, which

are involved in emotional regulation (Mato et al., 2003).

Similarly, both endocannabinoids AEA and 2AG are found

in the fetal brain, with concentration levels varying through-

out the perinatal period. That suggests an important role

of the endocannabinoid system during the development of

the fetal brain (Friedrich et al., 2016). Many studies have

conﬁrmed that CB1Rs and endocannabinoids play crucial

roles during fetal development by controlling neurodevelop-

mental processes involved in the development of neurons

and synapses (Berghuis et al., 2007; Harkany et al., 2007;

Maccarrone etal., 2014; Mulder et al., 2008).

The characteristic lipophilic nature of cannabinoids allows

them to cross the placental and blood–brain barrier where

they can activate cannabinoid receptors (Park et al., 2003).

Therefore, exposure to exogenous cannabinoids in utero

may disrupt the fetal endogenous cannabinoid signal-

ling system and consequently the embryo development.

Supporting this idea, a study in humans has shown that

prenatal THC can directly and permanently impair the neur-

onal networks during fetal brain development, an effect

potentially mediated via CB1Rs (Tortoriello et al., 2014).

Studies in humans have also demonstrated that prenatal

cannabis exposure may lead to alterations in various

neurotransmitter (i.e., GABAergic 3, dopaminergic, gluta-

matergic, serotonergic and opioidergic) systems in children

(Fernández-Ruiz et al., 2000; Jutras-Aswad et al., 2009;

Trezza et al., 2008).

Paternal Cannabis Use

Over the years, a growing interest in the effects of prenatal

paternal use of cannabis on offspring has emerged. For

example, the Generation R and ABCD cohorts pinpointed

that paternal cannabis use during the gestational period,

independently of maternal cannabis use, can be associ-

ated with the onset of psychotic-like experiences and other

behavioural disorders in middle childhood (Bolhuis et al.,

2018; Paul et al., 2021). Whether those effects are induced

by epigenetic mechanisms or other underlying etiological

factors remains unclear.

Studies in animals have provided further information about

the long-term effects of paternal cannabis use on offspring:

One study showed that adolescent THC exposure in rats

before mating can lead to lasting behavioural and neuro-

biological abnormalities on the next generation of rats that

have been unexposed to THC. This suggests that THC can

affect parental gametes and have lasting negative effects

on the next generation of rats (Szutorisz et al., 2014).

Supporting this idea, recent evidence coming from human

and animal studies suggested that paternal THC expos-

ure can alter sperm cells’ DNA methylation, therefore inﬂu-

encing offspring genes and development (Murphy et al.,

2018). Another study in rats found that while premating

paternal THC exposure did not have negative effects on

birth weight, survival and growth of the offspring, it induced

long-term attentional and cognitive deﬁcits when offspring

were tested at adolescence (Holloway et al., 2020) or adult-

hood (Levin et al., 2019).

Clearing the Smoke on Cannabis: Cannabis Use During Pregnancy and Breastfeeding

Therefore, besides potential direct in utero effects, pre-

natal THC exposure can impact the developing brain

and behaviour via action on gametes, or through epigen-

etic modiﬁcations such as DNA methylations or histone

replacement that can modulate gene expression and inﬂu-

ence protein production (Cholewa-Waclaw et al., 2016;

Maze et al., 2014). Further studies need to be conducted

to better understand epigenetic mechanisms potentially

associated with behavioural and developmental disorder

outcomes in offspring exposed to maternal or paternal

cannabis use.

Effects of Cannabidiol During Pregnancy

The effects of CBD use during pregnancy or breastfeeding

are unknown. Both clinical and preclinical studies evaluat-

ing the safety of CBD use during pregnancy are urgently

needed, especially with the widespread belief that CBD can

relieve symptoms associated with pregnancy (i.e., pain,

nausea, vomiting, anxiety).

CBD products often contain THC, which is known to have

negative effects on brain development. There is no clinical

evidence yet about the safety of using CBD during preg-

nancy, and only a few studies on animals have analyzed

the effects of CBD during pregnancy and lactation. For

example, in one older study on rodents, it was shown that

maternal exposure to CBD reduced spermatogenesis and

fertility in male offspring examined at adulthood (Dalterio

& DeRooij, 1986). In a more recent study, Wanner et al.

(2021) found that maternal use of CBD in mice induced

long-term anxiety and cognitive deﬁcits in females but not

in male offspring. These effects were associated with chan-

ges in genes through epigenetic modiﬁcations that play

important roles in neuronal function and are known to be

involved in psychiatric and neurodevelopmental disorders.

This preclinical study was the ﬁrst to identify potential long-

term negative effects induced by maternal prenatal CBD in

female offspring.

Further studies are needed to better evaluate the effects

of CBD use during pregnancy and breastfeeding. While

we are waiting for more robust studies, the Society of

Obstetricians and Gynecologists of Canada (2022) recom-

mended that women should not use cannabis or CBD dur-

ing pregnancy or breastfeeding.

Conclusions and Implications

Brain development involves a complex cascade of events

inﬂuenced by prenatal, physical, social and emotional

factors early in life, which can have long-lasting effects

on behaviour (for reviews, see Finnegan, 2013; Leyton &

Stewart, 2014). Maternal cannabis use can directly affect

the prenatal brain and signiﬁcantly disrupt neural develop-

ment, leading to adverse effects on child development and

brain function, including cognition, emotions and memory

impairments. Cannabis use during pregnancy and breast-

feeding does not appear to be harmless, and there is grow-

ing evidence showing some risks associated with cannabis

use on fetal development. Indeed, the evidence shows that

prenatal cannabis smoking (particularly heavy exposure)

has adverse effects on cognitive functioning, behaviour,

mental health and substance use beginning as early as age

three years and during adolescence.

However, there are some limitations in the available data.

First, many studies do not indicate a gestational age of

exposure, cannabis type, frequency of use, dose and

method of use, and they often rely on self-reported can-

nabis use, which can be inaccurate or underreported. Self-

reports of cannabis should be validated in further studies

using urine toxicology tests.

Conclusions about the effects of prenatal cannabis expos-

ure can be confounded by other maternal risk factors that

tend to occur more frequently in women who use canna-

bis. These factors include lower prenatal care access, poor

nutrition, poor physical and mental health, lower socio-

economic status, lower levels of education and the use

of other substances. Negative perinatal outcomes appear

more pronounced in infants when mothers smoked both

cannabis and tobacco compared with the use of either

substance alone, suggesting an additive effect of using

cannabis with tobacco (Chabarria et al., 2016; El Marroun

et al., 2009). While not yet corroborated by evidence in

humans, animal studies also suggest that cannabis and

alcohol during pregnancy can also have synergistic effects

(Hansen et al., 2008; Seleverstov et al., 2017; Subbanna

et al., 2018).

While prospective longitudinal studies are better able

to assess and adjust for some of these factors to parse

out direct associations with prenatal cannabis exposure,

some other studies do not. Because of the existence of

other potential confounders, the effects of prenatal canna-

bis exposure can be difﬁcult to attribute only to cannabis,

so data should be interpreted with caution. Future stud-

ies should assess and control for confounding variables

that can potentially inﬂuence the development of pre-

natally exposed offspring. Additionally, most of the studies

reported only positive correlation or associations between

prenatal cannabis use and offspring negative outcomes.

Positive correlation or association does not mean causal

association. Findings from studies should be interpreted

with caution.

Clearing the Smoke on Cannabis: Cannabis Use During Pregnancy and Breastfeeding

Over the years, cannabis THC content from smoked can-

nabis has considerably increased from 3% to 6% in prior

decades to 5% to more than 15% (Hall et al., 2019).

Discrepancies in ﬁndings about birth, behavioural and

developmental outcomes among studies might be attrib-

uted to the increasing potency of cannabis over the past

few decades (ElSohly et al., 2016; European Monitoring

Centre for Drugs and Drug Addiction, 2017; University of

Mississippi, National Center for Natural Products Research

[as cited in Executive Ofﬁce of the President of the United

States, 2013]; Mehmedic et al., 2010). This possibility is

especially relevant for comparisons among the OPPS,

MHPCD and the more recent Generation R studies as the

children enrolled in the latter study may have been exposed

to higher levels of THC.

In addition, authorized retail cannabis stores can be of

concern because of varying THC levels in the available

products. For example, in some cannabis concentrates

made by extracting THC from the plant such as kief, hash

or resin, THC content ranges from 39% to 90%. However,

the legalization of nonmedical cannabis allows consumers

to know exactly the content of the product they are using

and select lower-risk products (e.g., containing less THC).

On the illegal market, there is no guarantee of the THC lev-

els nor any other potentially harmful contaminants. Strong

evidence-based information should be incorporated into

the training of retail cannabis staff, so they can better inform

customers about the potential effects of cannabis use dur-

ing pregnancy and breastfeeding. However, there is no

determined amount of cannabis exposure that is safe. Until

the effects of prenatal cannabis exposure are well under-

stood, the safest option available to pregnant women is to

avoid using cannabis (Best Start Resource Centre, 2017;

Canada FASD Research Network, 2017).

Growing evidence from human and animal studies has

shown that both maternal and paternal cannabis use can

have negative outcomes on offspring neurodevelopment,

and these effects can be linked with the existence of shared

etiological factors, such as genetic and environmental,

familial behaviours, lifestyle habits of the parents and so on.

Further robust clinical studies with both parents along with

increased awareness of potential health outcomes associ-

ated with prenatal cannabis use are crucial to understand-

ing the potential risks of cannabis use during pregnancy.

Cannabis use for therapeutic purposes, including CBD use,

during pregnancy or lactation is also not recommended.

In addition, while consuming cannabis in edible or vapor-

ized forms eliminates the risks of smoking, the child will

still be exposed to the components of cannabis (Colorado

Department of Public Health and Environment, 2017). The

Society of Obstetricians and Gynecologists of Canada (2022)

recommends that women should not use cannabis or CBD

products during pregnancy or breastfeeding. An investment

in public education efforts to increase awareness of the

effects of cannabis use during pregnancy is needed. This

investment would be useful considering that online media

frequently report beneﬁts of cannabis or CBD use that are

not consistent with scientiﬁc evidence. Such reports include

the portrayal of cannabis use as helpful for pregnancy symp-

toms, such as morning sickness (Jarlenski et al., 2018).

Implications for Healthcare Professionals

Despite the high prevalence of cannabis use among

women of childbearing age, the potential affect of canna-

bis on the developing brain and the long-term inﬂuence on

cognition, behaviour and mental health are still not well-

appreciated by society. Healthcare professionals who pro-

vide care to pregnant women should be well informed of

the latest clinical evidence and research to advise pregnant

women and those of childbearing age of the potential risks.

Healthcare professionals need to explore these issues with

patients and provide unbiased, compassionate information

to women and their partners. Appropriate counselling ser-

vices should also be offered to nursing mothers who are

using cannabis as the beneﬁts of breastfeeding can still

outweigh the possible harms of exposure from occasional

cannabis use (Djulus et al., 2005; Garry et al., 2009).

However, there are growing concerns that the medical

community does not have sufﬁcient guidance for address-

ing maternal cannabis use during pregnancy nor breast-

feeding, and there is a strong need for training in the

management of cannabis use during pregnancy. Improved

communications and guidance from healthcare providers

and resources addressing maternal cannabis use during

pregnancy or breastfeeding are therefore strongly needed.

There is also a need for person-centred, harm reduction

and trauma-informed approaches to discuss cannabis use

during pregnancy and breastfeeding and building a non-

judgmental and trusting relationship between healthcare

providers and pregnant parents.

Prevention efforts aimed at reducing prenatal cannabis

exposure could be aided by clinical guidelines developed for

healthcare practitioners about discussing the health effects

of cannabis use during pregnancy and breastfeeding,

such as those available in Colorado (Colorado Department

of Public Health and Environment, 2017). The Society of

Obstetrician and Gynaecologists of Canada is working on

clinical guidelines that will provide healthcare workers with

the latest evidence on cannabis use and women’s health,

Clearing the Smoke on Cannabis: Cannabis Use During Pregnancy and Breastfeeding

with a focus on women who are planning a pregnancy, who

are pregnant or who are breastfeeding.

Implications for Researchers

More research on both maternal and paternal cannabis use

during pregnancy is needed. Knowledge gaps exist about

reporting quantity and quality of cannabis used, CBD effects,

impact of consumption method, timing of use in pregnancy

and effect on breastfeeding. The changing landscape,

including increased accessibility to cannabis, decreased

perceptions of risk, increased THC concentrations in can-

nabis and the advent of potent synthetic cannabinoid prod-

ucts, needs to be examined. Finally, research and preven-

tion efforts should explore the role played by the parental

determinants of health (Brown et al., 2016; Havens et al.,

2009; Passey et al., 2014). Addressing these comorbid con-

ditions needs to be part of a holistic approach to reducing

the risks associated with cannabis use during pregnancy

and breastfeeding.

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Acknowledgements

The author thanks the external reviewers for their comments on an earlier version of this report. Production of this docu-

ment has been made possible through a ﬁnancial contribution from Health Canada. The views expressed herein do

not necessarily represent the views of Health Canada.