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