Potent Marijuana Tied to Psychosis Risk

Marijuana bred to contain high levels of THC could raise the risk of developing psychosis, according to researchers from the U.K.

Reuters reported Nov. 30 that researchers Marta di Forti and colleagues from King’s College London compared users of potent “skunk” marijuana to users who smoked cannabis resin (“hash”) and found that the incidence of psychotic illnesses like schizophrenia was almost seven times higher among the skunk users.

“The risk of psychosis is much greater among people who are frequent cannabis users, especially among those using skunk, rather than among occasional users of traditional hash,” said di Forti.

The study, based on a comparison between 280 individuals who has suffered their first psychotic episode and 174 healthy controls, also found that individuals who had suffered psychosis severe enough to result in a hospital admission and last a week or more were twice as likely to be long-term marijuana users and six times more likely to be daily users of the drug.

In London, where the study was conducted, “skunk” marijuana contains about 12-18 percent THC, compared to 3.4 percent THC in traditional cannabis resin.

The findings were published in the December 2009 issue of the British Journal of Psychiatry.