Consequences of Prenatal Drug Exposure: Marijuana


Epidemiology of Marijuana Use in Pregnancy

In a recent NIDA survey (1996) of the prevalence and patterns of substance use among pregnant women, 2.8 percent reported marijuana use during their first trimester of pregnancy. This indicates that marijuana is the most commonly used illicit drug and, after alcohol and tobacco, the most commonly used drug during pregnancy. As Fried observed (), this makes the paucity of objective information on the relationship between marijuana use during pregnancy and the impact of such use upon the outcome of the child all the more striking.

Growth Effects

Of the longitudinal studies of marijuana use during pregnancy, most find few significant effects on growth parameters. Day and colleagues () obtained neonatal outcome data on more than 500 infants born prenatally exposed to varying amounts of marijuana in utero. There were few significant effects of marijuana use during pregnancy on birth weight, head or chest circumference, gestational age, or growth retardation. There was a small but significant negative effect of marijuana use during the first two months of pregnancy on birth length and a positive effect of marijuana use during the third trimester on birth weight. In a more recent study of growth from birth to early adolescence in offspring prenatally exposed to marijuana, this exposure was not significantly related to any growth measure.

Behavioral Effects

Much of the existing information concerning the behavioral effects of prenatal exposure to marijuana comes from reports of the Ottawa Prenatal Prospective Study (OPPS) and the work of Nancy Day and her colleagues (). The first report from the Ottawa study examined four-day-old infants born to regular marijuana users and found that prenatal exposure to marijuana was associated with decreased rates of visual habituation and increased tremors. Similar observations were also noted at nine and 30 days of age. When these same children were examined at one year of age, no adverse effects of prenatal marijuana exposure were noted. Fried et al. () noted the difficulty in unraveling the long-term consequences of in utero marijuana exposure. Although some observations of a neurobehavioral effect on verbal ability and memory of four-year-old subjects was noted, this relationship did not persist at ages two, three, five, or six years after statistically adjusting for other important variables such as ratings of the home environment.

Arousal Regulation and Attention

A few research findings indicate that prenatal marijuana exposure has an effect on child behavior problems at preschool and school age. In a prospective study of the effects of prenatal marijuana exposure on child behavior problems at age ten, prenatal marijuana exposure in the first and third trimesters predicted significantly increased hyperactivity, inattention, and impulsivity symptoms. These results are consistent with the work of O’Connell and Fried () who found a significant tendency for mothers who used marijuana heavily during pregnancy to rate their children as being more impulsive or hyperactive. The authors note, however, that it remains to be seen whether these results indicate a true behavioral difference in the attention-related domain or a lowered parental tolerance.

Social and Environmental Considerations

According to Goldschmidt et al. (), it is difficult to isolate the effects of marijuana exposure from its correlates and from environmental risk factors. Variables such as socioeconomic status, access to medical and social services, and the presence or absence of a male figure in the household have a significant influence on child development. Maternal mental health, social support networks, stressful life events such as exposure to violence or domestic abuse are also important variables that impact long-term developmental outcomes. Many of these environmental risk factors are directly associated with maternal marijuana use, making it difficult to identify the impact of prenatal exposure in isolation.


After statistically controlling for maternal personality and home environment conditions, many of the neurobehavioral consequences of prenatal exposure to marijuana do not remain significant. According to Fried (), the only definitive statement regarding prenatal exposure to marijuana would be that, if there are long-term consequences of prenatal exposure to marijuana, such effects are very subtle. At this point there are few human studies on the effects of marijuana use during pregnancy and no precise mechanism of action has been substantiated.


Selections from the book: “Handbook of the Medical Consequences of Alcohol and Drug Abuse” (2004)