Heavy Marijuana Use Linked To Schizophrenia-Like Brain Changes In Teens, Uh Oh

Headlines heralding the link between marijuana, mental illness, and brain damage seem more apropos of the Reefer Madness era than these medical marijuana-mad times. But a new study is raising alarm: it finds that structural brain changes in teen marijuana smokers resemble those seen in schizophrenics. According to the study — published in the journal Schizophrenia Bulletin — chronic smokers (teens who smoked pot daily for about three years) performed poorer on memory tests and showed shrinkage in brain areas related to working memory. These brain changes also looked similar to schizophrenia-related abnormalities, the researchers say.

The younger an individual was when they started smoking pot, the more brain abnormalities that were seen. "These ... appear to last for at least a few years after people stop using it," said lead study author Matthew Smith, a psychiatry professor at Northwestern University. It's possible, however, that these structural differences trigger a tendency to smoke pot, rather than pot causing the brain changes, he said.

Heavy marijuana use has been linked to schizophrenia in some prior research, though other studies have shown cannabis compounds might help relieve symptoms of schizophrenia. Marijuana use is nearly twice as common in schizophrenics than in the general population, though of course there's also a question of cause and effect here (people genetically susceptible to schizophrenia may also especially enjoy getting stoned).

Skeptics of the link point out that marijuana use has risen greatly over the past century, with no corresponding surge in schizophrenia. In a 2012 review of the evidence, researchers concluded that "there is strong evidence to support the hypothesis that cannabis consumption is a risk factor" for schizophrenia, but only in young adult pot smokers. Fifteen to 18-year-old marijuana smokers had more schizophrenia symptoms, but this increased likelihood was no longer significant by age 26.