Marijuana is the world’s most widely used illicit drug. But smoke too many joints too soon, and you might lose IQ points: A new study suggests extensive marijuana use starting as a teenager could lead to cognitive decline.
In a study of 1,037 New Zealanders followed from birth to age 38, people who began using marijuana as adolescents and used it extensively for years saw their IQs drop by about eight points. What’s more, among adolescent-onset users, quitting the drug did not reverse the mental deficits.
Marijuana is not harmless, and particularly not for adolescents. To get a sense of how significant a decline of eight IQ points is, consider this: Having an average IQ of 100 puts you in the 50th percentile for intelligence, whereas an IQ of 92 slides you down to the 29th percentile. Learn more here, here or here.