Most of the long-term effects of marijuana use that are summarized here have been observed among heavy or long-term users, but multiple (often hidden) confounding factors detract from our ability to establish causality (including the frequent use of marijuana in combination with other drugs). These factors also complicate our ability to assess the true effect of intrauterine exposure to marijuana. Indeed, despite the use of marijuana by pregnant women,48 and animal models suggesting that cannabis exposure during pregnancy may alter the normal processes and trajectories of brain development,49 our understanding of the long-term effects of prenatal exposure to marijuana in humans is very poor.
