The dominant narrative about marijuana seems to be that it is harmless. Indeed, 19 states and D.C. have legalized recreational marijuana, and young people are increasingly nonchalant about using it. One study shows nearly half of college students said they consumed marijuana. Eight percent reported they used it daily or nearly every day. One in 5 high school students used marijuana in the preceding 30 days.

But there are real dangers associated with the substance, as a 2020 report from the National Institute on Drug Abuse (NIDA) shows. Abundant research demonstrates how exposure to marijuana during childhood impacts later cognitive ability, including memory, attention, motivation and learning. Studies have linked regular cannabis use in adolescents with lower IQs in adulthood and higher propensity to drop out of high school. This association persists in college-age students. One large study followed college students and found frequency of marijuana use to correlate with skipping classes, lower grade-point average and longer time to graduation.

Some studies have also linked frequent cannabis use in youths to increased rates of schizophrenia, depression and anxiety. One Lancet article reported that smoking high-potency marijuana every day increased the chance of developing psychosis by nearly five times.

More research is needed on whether the causality could be the other way around — perhaps those predisposed to mental health diagnoses are more likely to seek out marijuana. But as Nora Volkow, a psychiatrist and the director of NIDA, told me, “Based on the data we already have, we can clearly say that marijuana is not a benign drug, especially for children and adolescents.”