People who smoke pot may be at increased risk for psychosis if they have a certain genetic marker, a new study finds.
The results show people with this genetic marker who use cannabis are twice as likely to experience psychosis compared with those who use the drug but do not have the genetic marker.
Among people who use the drug every day, the risk for psychosis increases sevenfold for those who have the genetic marker.
Previous studies have linked smoking marijuana with an increased risk of psychiatric disorders, such as schizophrenia, but only a small number of those who smoke pot will ever have a psychotic episode. The new finding could help identify which cannabis users might be at risk for this side effect, the researchers said.
"Our findings help to explain why one cannabis user develops psychosis while his friends continue smoking without problems," said study researcher Dr. Marta Di Forti, of King's College London's Institute of Psychiatry.
The study involved 489 people living in London who had experienced a psychotic episode, and 278 healthy people without a history of psychiatric disorders. [6 Foods that Are Good for Your Brain ]
The genetic marker in question is one variation of a gene call AKT1. The new finding confirms earlier research, which also linked this marker with the risk of psychosis after smoking pot.
The AKT1 gene is known to be involved in the signaling of the brain chemical dopamine, which is abnormal in those with psychosis, Di Forti said.
The genetic marker likely acts along with other genes to contribute to the risk of psychosis from cannabis smoking, the researchers said. Finding the genetic underpinnings of cannabis psychosis may lead to the development of therapies for the condition, said Dr. John Krystal, editor of Biological Psychiatry, the journal in which the study was published Nov. 15.