Daily Weed Smoking Increases Risks of Psychosis, Study Finds

smoking weed linked to risk of developing psychosis

A new study that links the risks of developing psychosis and the long-term smoking of high-potency marijuana may have stoners a bit paranoid. According to a new study published this week in Lancet Psychiatry, daily or high-potency marijuana use increases the risks of developing a psychotic disorder.

The study, published this week in Lancet Psychiatry, assessed more than 900 people in multiple cities across Europe, all of whom had been diagnosed with at least one episode of psychosis. Researchers surveyed study participants about their cannabis-smoking habits, asking them questions about when they started using it, how often they used it, and what kind of strains they smoked. Then, researched compared the results against a control group of 1,100 people who had never experienced an episode of psychosis.

Researchers say they found that people who smoked weed every day were three times more likely to have a psychotic episode than those who had never passed the dutchie on the left-hand side.

Risks of developing a psychotic episode went up among study participants who began smoking weed at a younger age or smoked high-potency weed (defined in the study as anything that contained more than 10 percent THC).

"Psychotic disorder," precisely, is what was studied, said Dr. Marta Di Forti, lead author and a clinician scientist at the Institute of Psychiatry, Psychology & Neuroscience, King's College London. "We are talking about people who meet diagnostic criteria [and] come to the attention of mental health services to receive treatment for psychosis. So they have to have symptoms of psychosis across the spectrum -- so hallucination, delusion -- that have lasted at least for a week."

New study warns heavy pot users of links to psychosis

NORML, an organization that advocates for the change in marijuana laws across the U.S. responded to the latest study, writing that the results were "premature at best" and "sensational at worst to claim that a casual relationship exists between marijuana use and psychiatric disorders" based on the new paper.

NORML also points out that participants often use other intoxicants in at greater rates than the general public and that people pre-disposed to psychotic episodes are self-medicating with marijuana.

The organization also points out that the study used participant's self-reported data, a methodology that was flawed in that researchers had no way to test the potency of the weed consumed by study participants. Because the study was conducted in cities like London and Paris, where the substance is illegal, the marijuana was likely purchased through the black market, and could have exposed study participants to any number of molds or pesticides.

As more states across the United States legalize medical and recreational marijuana, the new study demonstrates the need for more research on the link between long-term marijuana use and mental health.

Photos: Getty Images

Jeff St. Pierre

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