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Because alcohol and tobacco have long been legal substances, there is a lot of evidence about their use during the preconception, pregnancy and perinatal periods. With the legalization of cannabis in Canada, new research on cannabis use may begin to fill the existing evidence gaps and better define its risks.

Because of its illegal status, women may have been reluctant to report using cannabis during pregnancy unless it was being used medically, and research ethics may have prohibited its study. Consequently, much of what we know about cannabis use in pregnancy has come from data gathered during studies on alcohol and tobacco. That is why it now makes sense to link the work of all three substances.

For instance, research shows that women who use cannabis during pregnancy are more likely to smoke cigarettes and use alcohol.1 As well, co-use of tobacco and cannabis is associated small head circumference and may increase other birth defects (cardio, musculoskeletal, and gastrointestinal) compared to no-use and single-use groups.2 This finding of association should be interpreted with some caution based on the number of limitations of the study. Still, it does underscore the need for more robust research in order to understand the association.

Researching all three substances allows for understanding the “clustering of risks” and the interactions between those risks in a way that targeting individual substances cannot do.3 By looking at the clustering of risk as described by researchers, holistic prevention efforts can target social determinants of health that affect poly-substance use.

Linking the findings on the three substances allows researchers to parse out the differences among those who use substances in pregnancy, and the clusters of risk for the substances they use. That will help to further prevention efforts in messaging, discussing substance use with women and their partners, and supporting women with holistic and safe approaches.


1. Ko, J.Y., Tong, V.T., Bombard, J.M., Hayes, D.K., Davy, J., & Perham-Hester, K.A. (2018). Marijuana use during and after pregnancy and association of prenatal use on birth outcomes: A population-based study. Drug and alcohol dependence, 187, 72-78.
2. Coleman-Cowger, V.H., Oga, E.A., Peters, E.N., & Mark, K. (2018). Prevalence and associated birth outcomes of co-use of Cannabis and tobacco cigarettes during pregnancy. Neurotoxicology and teratology, 68, 84-90.
3. Passey, Megan E. et al. (2014). Tobacco, alcohol and cannabis use during pregnancy: Clustering of risks. Drug & Alcohol Dependence, Volume 134, 44–50.

For more on these topics, see earlier posts:



While illicit drug use during pregnancy seems to get a larger share of sensationalistic media headlines, research over the past two decades has consistently shown that tobacco and alcohol (the “legal drugs”) are the ones that can cause the most harm during pregnancy.

A recent study by James Janisse and colleagues in Detroit, Michigan looked at this issue by examining the individual and combined impact of alcohol, tobacco, cocaine, and marijuana on low birth weight. (Low birth weight can be caused by a number of factors, including substance use, and is considered an indicator of infant mortality and of later concerns like learning difficulties, hearing and visual impairments, asthma and other chronic diseases).

The researchers found that each of the drugs – alcohol, tobacco, marijuana, and cocaine – had independent and negative effects on outcomes (after controlling for factors like infant sex and mother’s weight). Each of the four substances differed in terms of the way they impacted infant birth weight. For cocaine, the entire effect was due to decreased gestational age at birth, with no direct impact on fetal growth. For marijuana, the entire effect was due to restricted fetal growth. Alcohol and cigarettes both shortened gestational duration and restricted fetal growth.

One of the major findings was that the comparative effect of alcohol, cigarette, cocaine, and marijuana use on birth weight varied by maternal age. For younger women, pregnancy alcohol, cigarette, and cocaine use had a somewhat similar effect on birth weight, with cocaine and smoking having nearly double the impact of marijuana. In contrast, for women aged 30, the impact of alcohol use on birth weight was nearly double that of cocaine use and triple that of marijuana use.

Overall, it was the use of alcohol and/or cigarettes that was clearly more harmful to fetal growth than cocaine use.


Bailey, B.A., McCook, JG., Hodge, A. and McGrady, L. (2012). Infant birth outcomes among substance using women: why quitting smoking during pregnancy is just as important as quitting harder drugs. Matern Child Health J, 16:414–422.

English, D.R., Hulse, G.K., Milne, E., Holman, C.D. and Bower, C.I. (1997). Maternal cannabis use and birth weight: a meta-analysis. Addiction, 92:1553–1560.

Janisse, J.J., Bailey, B.A., Ager, J., and Sokol, R.J. (2014). Alcohol, Tobacco, Cocaine, and Marijuana Use: Relative Contributions to Preterm Delivery and Fetal Growth Restriction. Substance Abuse, 35(1): 60-67, DOI: 10.1080/08897077.2013.804483


The Canada Prenatal Nutrition Program (CPNP) consists of approximately 330 community-based projects in about 2,000 communities across Canada. The goal of the program is to support pregnant women facing challenges that put their health and the health of their infants at risk. These challenges can include poverty, teen pregnancy, social and geographic isolation, substance use and family violence. The CPNP also provides culturally sensitive prenatal support for Aboriginal women and recent immigrants.

Operating since 1994, the program serves approximately 50,000 women a year. It encompasses a comprehensive range of services,  including nutrition counseling; provision of prenatal vitamins, food and food coupons; prenatal health and lifestyle counseling; breastfeeding education and support; food preparation training; education and support on infant care and child development; and referrals to other agencies and services.

Evaluation of the Canada Prenatal Nutrition Program has been ongoing since it started (see more here), but I was interested in the findings of a study published in the Canadian Journal of Public Health which used an innovative approach to looking at the impact of the program on women and their infants. Because it is not possible to compare the outcomes of women who participated in the program with a similar group of women who did not participate in the program (i.e., with a “control group”), the researchers compared women who received a higher “dose” of CPNP services with those receiving a lower “dose” of CPNP services. They looked at three aspects:

  1. program initiation (when in her pregnancy a woman started attending the program);
  2. program intensity (number of contacts a woman had with the program); and
  3. program duration (number of weeks a woman was involved in the program).

Overall, women with a higher CPNP “dose” tended to make more positive health behaviour changes and to have fewer negative birth outcomes than those with overall low exposure to the program. They were more likely to reduce the number of cigarettes they smoked and to cease drinking; to breastfeed their infants and to breastfeed for longer; and to increase the use of vitamin/mineral supplements from never to daily.

In terms of tobacco and alcohol use, over three quarters of women were smokers at program entry, most smoking fewer than 20 cigarettes a day. Slightly more than half were exposed to second-hand smoke during their pregnancy. More than 40% of women indicated that they had consumed alcohol since becoming pregnant, over half of whom reported having at least five drinks in one day.

The majority of women (84.2%) reported quitting drinking during pregnancy; women who scored ‘high’ on overall CPNP exposure were 42% more likely to quit drinking. Earlier program initiation, higher program intensity, and longer program duration were all related to a higher likelihood of cutting out alcohol during pregnancy.


Muhajarine, N., Ng, J., Bowen, A., Cushon, J., and Johnson, S. (2012). Understanding the Impact of the Canada Prenatal Nutrition Program: A Quantitative Evaluation. Canadian Journal of Public Health, 103(7 Suppl 1): eS26-31. Download free full-text here.

Muhajarine N., Ng , J., Green, K., Bowen, A., Cushon, J., Johnson, S., and Macqueen, Smith F. (2009). Understanding the Impact of the Canada Prenatal Nutrition Program: A Quantitative Evaluation. Submitted to the Public Health Agency of Canada (PHAC). Saskatoon, SK: Saskatchewan Population Health and Evaluation Research Unit.

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