Discussion
We identified 23 studies that describe the perspectives of just over 10,000 pregnant people about the reasons for, risks and benefits of, and available information about cannabis use during pregnancy. We did not identify any studies about the perspectives of lactating people about using cannabis during lactation, nor did we identify any studies about the perspectives of partners on the use of cannabis during pregnancy or lactation.
This review demonstrates the powerful nature of the study design on research findings. When cannabis is included as one illicit drug used by someone enrolled in a substance abuse treatment program, the considerations and priorities are very different than when it is included as an herbal medicine used by someone seeking a non-pharmaceutical remedy for nausea and vomiting in pregnancy. Many studies did not describe the reasons why a person may seek to use cannabis during pregnancy, or the benefits that users experience from this substance. Most studies focused on smoked cannabis, and do not investigate perceptions of risks other forms of cannabis products (e.g. oils, topical applications, low-THC products).
Concern with fetal harm from prenatal cannabis exposure is a common theme in this literature. Strikingly, cannabis is almost always compared by study authors to substances where strong evidence of fetal harm exists (e.g., alcohol, tobacco, methamphetamines, opioids). This comparison is carried through to public health and clinical materials which also commonly group cannabis with these substances, belying the emergent and equivocal nature of evidence of fetal harm. These common groupings illuminate the assumptions of researchers but make it difficult to see that pregnant people may not understand cannabis the same way. For example, in one included study, participants compared cannabis to caffeine and fast food, two substances which are sub-optimal, but fulfill important social and emotional functions for pregnant people 20.
The precautionary principle holds that when evidence is uncertain, the appropriate course of action is to err on the side of caution73. Given the evidence showing the potential for deleterious effects of cannabis use during pregnancy and lactation, the ideal outcome would be to reduce or eliminate cannabis consumption during these periods. However, as participants in many of the included papers described, many receive benefits from using cannabis and fear that ceasing use may result in greater harm.
Clinicians working with pregnant people who are considering cannabis use may wish to adopt a harm reduction approach. Harm reduction is particularly relevant in obstetrical settings where the decision-maker is not the only person affected by choices about substance use. A harm reduction approach accepts the inevitability of drug use and works with users to minimize the associated harms 74. Given the documented perceptions of benefit and the lack of certainty about harm of cannabis use in pregnancy, we encourage clinicians and researchers to inquire about why a person wishes to use cannabis, what benefits they receive from use. Discussions of risk and benefit should go beyond physiological impact and include the availability of support, personal care, agency, and emotional health 75. A strong relationship between clinicians and their pregnant clients will be beneficial in order to identify appropriate strategies for harm reduction, which may include reducing or quitting use, substituting other drugs or treatments, making a lifestyle change and seeking consistent prenatal care 74, 76.