Abstract
Cannabis is one of the most commonly used substances in Canada with 15% of Canadians reporting use in 2019. There is emerging evidence that cannabis is linked to an impact on the developing brain in utero and adverse outcomes in infants, children, and adolescents. The impact of cannabis during breastfeeding has been limited by studies with small sample sizes, follow-up limited to 1 year and the challenge of separating prenatal exposure from that during breastfeeding. In the absence of high-quality evidence, health care providers need to continue to engage women in conversation about the potential concerns related to breastfeeding and cannabis use.
Keywords: Cannabis, Breastfeeding, Infant nutrition, Substance use, Postpartum, THC
Cannabis is one of the most commonly used substances by Canadians. In 2019, the National Cannabis Survey reported that 15% of Canadians reported use in the previous 12 months (1). Cannabis use was recorded in 1.4% of 2012 to 2017 antenatal records in Ontario (2) which is likely an underestimate. Antenatal records from British Columbia demonstrated an increase in reported cannabis use from 2.2% in 2008 to 3.3% in 2016 (3). Importantly, certain groups have higher rates of cannabis use during pregnancy. For example, in British Columbia, rates were higher among younger women, those who admitted consuming tobacco, alcohol, or illicit drugs and those with mental health issues (3). Of those reporting use, 49.8% were 24 years of age of younger while only 1.2% were 40 years or older (3). The increased rates of reported use over time and the characteristics of women consuming cannabis are concordant with similar data from Colorado (4) where 10.2% admitted to continuing cannabis while breastfeeding (4). Postnatal cannabis use appeared to be associated with a shorter duration of breastfeeding with only 58% of cannabis using women continuing breastfeeding past 9 weeks postpartum compared to 79% of women who did not use cannabis postnatally (4). The use of cannabis during breastfeeding has not been well documented in Canada but is probably similar.
Cannabis has two well-known active substances, delta-9-tetrahydrocannibol (THC) and cannabidiol (CBD). THC has psychoactive properties and is the component most associated with euphoria. CBD has been less well studied but has fewer psychoactive properties. While cannabis can be inhaled, eaten, vaped, or used as an oil, the majority of the studies focus only on inhaled cannabis (5,6) and more specifically on the THC component. There is a variability in the percentage (level) of THC in cannabis used by consumers (7). THC being consumed may be at different percentages than expected by consumers. More importantly, the percentage of THC in consumer products has been increasing over time so that studies conducted in the past may reflect lower THC percentages compared to currently available cannabis (7). This is critical in accounting for dose dependent effects. Adding further challenges, cannabis may be used for recreational purposes and/or medical reasons and may be sourced from regulated producers, nonregulated producers, or illicit sources with the result being that the percentage of THC in a given product is typically not predictable.
Understanding the impact of cannabis consumption during breastfeeding requires an understanding of outcomes that may be related to THC consumed during pregnancy, the amount of THC available in breastmilk, and, finally, the few existing studies that examine the impact of combined breastfeeding and cannabis use.
OUTCOMES RELATED TO CANNABIS USE DURING PREGNANCY
The impact of cannabis use during pregnancy has been reported in studies in the immediate newborn period spanning into early adulthood (8–12). Three longitudinal studies have followed infants to examine the impact of cannabis use during pregnancy on children, adolescents, and young adults. Cannabis use during pregnancy has been associated with negative outcomes ranging from decreased birth weight to poorer neurocognitive outcomes including deficits in executive functioning, verbal skills, attention, and school-related performance (8–12). All three of these longitudinal studies examined the impact of inhaled cannabis only and controlled for factors related to the sociodemographic factors. Inhaled cannabis is linked to an impact on the developing brain in utero and adverse outcomes in infants, children, and adolescents.
THC IN BREASTMILK
While it is challenging to measure THC levels in breastmilk, studies have demonstrated that at least some THC passes into breastmilk (13–15). THC levels in one study were present at measurable levels up to 6 days following cannabis use (14). Lipophilicity, dose consumed by the lactating woman, and frequency of use are factors that increase the concentration of THC in breastmilk (16). The mode of cannabis consumption may also change the concentration in breastmilk.
CANNABIS USE DURING BREASTFEEDING
A 1985 study from Colorado followed 756 pregnant women (17) of which 257 (34%) admitted some cannabis use during pregnancy. Infants were examined 24 to 72 hours after birth using a number of scales including Brazelton Neonatal Behavioral Scale, muscle tone, and Dubowitz scale for gestational age. The only significant difference between the cannabis exposed and nonexposed was shorter infant length in the cannabis exposed (which seems unlikely to be influenced by maternal cannabis consumption). At 1 year of age, 129 infants (38 born to women who admitted to daily cannabis use, 44 born to women with less frequent use, and 47 born to nonusers) were examined using the Bayley Infant Scale of Mental and Motor Development and Behavior Checklist. Of the 129 infants, 62 (48%) had been breastfed, of which 27 had been breastfed while the mother continued cannabis use. There were no differences reported for measures of growth or motor and mental development in the groups with prenatal, postnatal, or no cannabis exposure, but self-report of cannabis use may not be accurate and the small sample size may preclude identifying an effect. This study did not follow infants beyond 1 year of age.
In a 1990 study from Seattle, 68 cannabis exposed infants were matched to noncannabis-exposed infants based on the reported prenatal and postpartum tobacco and alcohol use (18). Two outcomes measures were used at 1 year of age: psychomotor developmental index (PDI) and mental developmental index (MDI) from the Bayley Scales of Infant Development. This study showed a decrease in PDI of 14 points associated with exposure to cannabis in breastmilk in the first month of life, which the authors remark would be clinically significant. Surprisingly, there was no similar decrease noted with exposure to breastmilk at the 3-month mark. There were no changes noted in the MDI at either time frame of exposure. The small sample size and the inability to control for exposure to cannabis, alcohol, and illicit substances during pregnancy present a challenge in interpreting this study.
A 1994 study from Jamaica reported on the neonatal outcomes for 24 infants exposed to cannabis both prenatally and during breastfeeding versus 20 controls (19). The outcomes measures were recorded at day 3 and at 1 month of age and were focused on neonatal adaptation using the Brazelton Neonatal Assessment Scale. There were no differences on day 3, but cannabis-exposed infants showed improved neonatal adaptation at 1 month of age. However, the sample size was small and there were important sociocultural differences between the two groups that might account for the difference (19).
In summary, the data on breastfeeding and cannabis are inconclusive. Studies did not analyze outcomes beyond the first year of life, only inhaled cannabis was studied, samples sizes were small, and the dose of cannabis was highly variable.
OTHER OUTCOMES IN THE FIRST YEAR OF LIFE RELATED TO ONGOING PARENTAL CANNABIS USE
A case–control study linked 239 infants who died of sudden infant death (SIDS) in southern California with matched controls (20). Only a small number of women reported cannabis use with breastfeeding in this study, but paternal use of cannabis seemed to be associated with an increased rate of SIDS (OR=2.8; P=0.04) even when controlling for the social determinants of health. Second-hand smoke from cannabis may also contribute to pulmonary disease. In addition, similar to alcohol use, cannabis use by parents can lead to impairment, resulting in suboptimal parenting.
DISCUSSION
There are no high-quality large studies of cannabis use during breastfeeding. There is some emerging evidence indicating some reduced growth and development in babies who have been exposed to cannabis via breastfeeding. One challenge in performing such studies is that mothers who are moderate or heavy users typically use cannabis during both pregnancy and breastfeeding, making it difficult to determine the additive effect of continuing use postpartum. Given the varied methods of consuming cannabis and the lack of a standard THC concentration in available products, it is difficult to determine how much cannabis mothers used. Many mothers are reluctant to report use of an illegal, or only recently legalized, substance.
ADVICE FOR PROVIDERS
A number of organizations have recommended, in the absence of good data to support the safety of cannabis during breastfeeding, that abstaining from use is prudent (21, 22). In the absence of high-quality evidence, health care providers need to continue to engage women in conversation about the potential concerns related to breastfeeding and cannabis use. There is emerging evidence that cannabis has a negative impact on the developing brain during pregnancy. It is reasonable to extrapolate that this continues during the newborn period. Exposure to second-hand smoke and parenting while impaired remain important topics of discussion irrespective of concerns about exposure of cannabis in breastmilk.
If women chose to consume cannabis while breastfeeding, reducing the amount of cannabis used including attention to a lower percentage of active ingredients is advised. Women who meet criteria for substance use disorders should be offered appropriate treatment options.
Funding: There are no funders to report for this submission.
Potential Conflicts of Interest: The author: No reported conflicts of interest. The author has submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed.
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