Of Reefer and Madness

Teens with a predisposition for psychotic illnesses such as schizophrenia may increase their risk by smoking marijuana, according to a new study. The findings cast light on how cannabis use affects developing brains and hints at new strategies for educating teens about pot's potential dangers.

Marijuana use and psychosis often go hand in hand, but the question of which causes which has been enshrouded in haze. Some evidence suggested that marijuana use might lead to psychosis, while other evidence hinted that people with a predisposition to psychotic illness are more likely to toke up. Hoping to clear the smoke, a team of researchers led by Jim van Os of Maastricht University in the Netherlands tracked marijuana use in healthy teenagers and other teens who reported symptoms such as paranoia, suggesting they were especially vulnerable to extreme psychosis.

The researchers surveyed more than 2400 Germans whose ages ranged from 14 to 24 years old, then followed up with the subjects 4 years later. After adjusting for factors such as socioeconomic status and the use of other drugs, the researchers found that among young adults with a predisposition for mental illness, those who smoked pot were more likely to develop severe psychosis than those who abstained. For kids with no predisposition to psychosis, smoking weed had a lesser effect, the scientists report online 1 December issue of the British Medical Journal.

"This is the first evidence that there is a causal chain of events, not just an association," says William Carpenter of the University of Maryland School of Medicine in Baltimore. He cautions however that the study doesn't resolve whether pot smoking actually causes an illness or just triggers its inevitable onset. The psychoactive components of reefer have been shown to amp up certain areas of the brain that have also been implicated in schizophrenia, and the researchers speculate that repeated smoking may have lasting affects on these pathways.

Rather than bombarding teens with messages about the evils of cannabis, it may make more sense to alert them to how their family history and biology can conspire with the choices they make, says van Os, especially when they are at an age where their brains are still developing.

Related links
Information on schizophrenia
Ethnobotany of Cannabis