Chances of developing psychosis are enhanced five times by smoking high-potency marijuana daily, a new study suggests.
The study from King's College London studied 901 people who had been diagnosed as having a first episode of psychosis at sites across Europe and Brazil between 2010 and 2015. When marijuana use was compared with a group of 1,200 patients deemed healthy, it was found that daily marijuana use was heavier among those who were encountering the psychiatric disorder.
"Differences in frequency of daily cannabis use and in use of high-potency cannabis contributed to the striking variation in the incidence of pscyhotic disorder across the 11 studies sites," the researchers state in their report.
The report from the United Kingdom comes as more U.S. states legalize marijuana. NORML, the marijuana decriminalization advocacy group, lists 10 states and the District of Columbia as having legalized pot use.
Marijuana overall has become more potent, experts warn.
Marijuana plants sold in the 1990s typically contained about 3 percent THC, the ingredient that leads to euphoric high that pot users hope to achieve in smoking or ingesting it, said Ziva Cooper, research director of the UCLA Cannabis Research Initiative earlier this month. These days, THC concentrations can be as high as 25 percent in weed sold at medical marijuana dispensaries.
The King's College study, published online in the journal Lancet, estimated that those who smoked pot on a daily basis were three times more likely than those who never used it to receive a psychosis diagnosis. Those smoking high-potency marijuana were five times more likely.