While most marijuana smokers don't suffer drug-linked psychotic episodes, some do—and the difference may come down to genetics. Users with a particular genetic marker face twice the risk of psychosis associated with the drug, a study finds; those with the marker who smoke pot daily are seven times more likely than other daily tokers to experience psychosis, LiveScience reports.
The genetic marker is a variation of the AKT1 gene, which happens to be linked to dopamine, a brain chemical that's abnormal among people with psychosis. "Our findings help to explain why one cannabis user develops psychosis while his friends continue smoking without problems," says an author of the London study, which observed 489 people who'd suffered psychotic episodes and 278 who hadn't. The study may contribute to future treatments for cannabis psychosis, says an expert.