Consequences of Marijuana Use: Reproductive Function


Hormones and Fertility

Research examining the effects of cannabis use on reproductive function in women or men has been sparse. In women, marijuana smoking can affect some reproductive hormones (e.g., luteinizing hormone, prolactin), but this effect may occur only when smoking takes place during specific phases of the menstrual cycle. Chronic cannabis use appears to alter male reproductive hormones, but these effects are not conclusive. Some studies have demonstrated marijuana-related decreased levels of gonadotropin, testosterone, prolactin, and luteinizing hormones in men, while others have reported negative findings. For both men and women the functional significance of these findings remains elusive. Although one might suspect that these purported effects on the reproductive system would adversely influence fertility, this has not been carefully studied in humans.

Perinatal Effects

Pregnant women who use cannabis expose the fetus to its effects, as THC is known to cross the placenta. Here we provide an overview of perinatal effects of cannabis use, focused primarily on cognitive functioning. It is estimated that 10 to 20 percent of women use marijuana during pregnancy. Thus, understanding the effects on fetal development is vital. Studying cannabis use during pregnancy in humans has proven difficult, as pregnant users generally have many additional risk factors for adverse effects such as tobacco smoking, alcohol use, other illicit drug use, poorer nutrition, and lower SES. Moreover, multiple factors deterring self-disclosure in this population raise concern regarding the validity of self-reports of cannabis use.

Studies have attempted to control for these confounds, hence, certain tentative conclusions appear justified. Risk of major congenital anomalies is not increased due to cannabis use in pregnant women. However, some reports suggest that risk of developing minor anomalies, particularly related to the visual system, may be related to heavy cannabis use, but these data are not robust. Cannabis use during pregnancy may be related to reduced birth weight and length, and possibly shortened length of gestation, although studies have reported conflicting findings. Overall, these perinatal effects, if valid, are clearly not as severe as those observed with tobacco smokers.

The cognitive and behavioral effects of prenatal exposure to cannabis are perhaps best addressed in one study, the Ottawa Prenatal Prospective Study (OPPS). This study collected birth data on 700 women and has periodically assessed the children of a subsample of 150 to 200. Adverse effects of prenatal cannabis use were observed in testing of the neonate during the first month. Possible indicators of an impact on the nervous system included increased tremors, decreased visual habituation, exaggerated startle, and increased hand-to-mouth behavior. However, at one and two years of age, no cannabis-related effects were observed when children were assessed using the Bayley Scales. No cannabis-related effects were observed at three years on tests of language expression, comprehension, and other general cognitive abilities, after controlling for confounding variables.

Age four assessments of OPPS children revealed cannabis-related performance decrements on verbal and memory tasks. These deficits were similar in type to another study of three-year-olds whose mothers smoked marijuana while pregnant. One hypothesis for why impairment was not observed until age four is the possibility that such deficits may not be detectable until individuals reach a developmental age that allows for testing of more subtle effects on complex processes. However, similar testing at five and six years did not reveal any cannabis-related deficits. The authors suggested that environmental exposure to positive influences on cognitive abilities (e.g., school) might have obviated the subtle effects observed a year earlier. Thus, the researchers initiated additional testing of six-year-olds to assess other, more general aspects of cognitive performance such as sustained attention and impulse control. Evidence of a deficit in sustained attention was observed in children whose mothers used marijuana heavily during pregnancy.

Testing at nine and twelve years of age showed marijuana-related deficits in measures of higher order or executive functioning that the investigators characterized as involving visual analysis, problem solving, hypothesis testing, and impulse control. Of note, these types of complex functioning deficits are similar to those observed in some studies of chronic adolescent and adult marijuana users. Goldschmidt and colleagues (2000) also reported adverse effects of prenatal marijuana use in ten-year-olds. Increased hyperactivity, impulsivity, inattention, and delinquency were associated with prenatal marijuana use after controlling for extraneous variables. Because of the limitations of their sample and other methodological issues, interpretation of these results warrants caution pending replication in other samples.

The observed effects of prenatal cannabis use on cognitive functioning appear subtle, and determining causality is difficult since genetic predispositions and multiple environmental factors after birth may interact with prenatal effects specific to cannabis use. The functional significance of these subtle deficits is also unclear; however, the types of impairment observed in the OPPS study could potentially affect general behavioral and cognitive performance abilities. Although these data are far from conclusive, they do raise concern regarding prenatal cannabis use and its effects on human offspring. As such, recommendations that pregnant women abstain from marijuana use appear warranted.

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