Massive Danish study finds strong link between marijuana addiction and mental illness

The study, published May 4 by the Cambridge journal Psychological Medicine, examines 6.9 million people ages 16-49 and more than 45,000 schizophrenia cases from 1972 to 2021. It found that the adjusted incidence risk ratio for males ages 16 to 20 was more than twice that for females of the same age group, concluding that “[a]t a population level, assuming causality, one-fifth of cases of schizophrenia among young males might be prevented by averting CUD” (cannabis use disorder).