Daily Cannabis Use May Up Risk for Developing Psychotic Disorder

Writing in the journal Lancet Psychiatry, Di Forti and an worldwide team of researchers report how they studied patient data - including cannabis use - collected between mid 2010 and mid 2015 for 901 adults under the age of 65 who arrived at mental health services in one of 10 locations in Europe, or one in Brazil, and received their first diagnosis of a psychotic disorder that was not down to, for example, brain tumours or acute drug use. The risk was three times greater among daily users, as compared with rare or nonusers, and higher still among daily users of high-potency cannabis.

The authors estimate that one in five new cases (20.4%) of psychosis across the 11 sites may be linked to daily cannabis use, and one in ten (12.2%) linked to use of high potency cannabis. In Amsterdam, where cannabis has been decriminalized for decades, the frequency of first-time psychosis diagnoses would decline from 38 people per 100,000 each year to 19 people per 100,000.

Currently, 10 states plus the District of Columbia allow recreational cannabis; 34 more states allow only medical use.

"The use of cannabis with a high concentration of THC has more harmful effects on mental health than the use of weaker forms", lead author Marta Di Forti of King's College London said in a statement.

Robin Murray, a professor at the IoPPN who also worked on the study, said it should be noted by all policymakers and any potential cannabis users.

Strong cannabis is that which contains a high level of delta-9-tetrahydrocannabinol, aka THC.

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Smoking high-potency marijuana every day could increase the chances of developing psychosis by almost five times, according to the biggest-ever study to examine the impact of pot on psychotic disorder rates.

These were then compared to 1,237 healthy adults to tease out the risk factors associated with psychosis.

"If you use cannabis, it doesn't mean you are definitely going to develop psychosis".

The researchers say the study does not prove a cause-and-effect relationship, but the association between mental health events and heavy marijuana use has been shown in previous studies. And 37 percent of people with first psychosis events used high-potency cannabis every day. It is perfectly possible that the association between cannabis and psychosis is bidirectional.

[2] Sites included in the study: London (UK), Cambridge (UK), Amsterdam (Netherlands), Gouda and Voorhout (Netherlands), Paris (Val-de-Marne, France), Puy de Dôme (France), Madrid (Spain), Barcelona (Spain), Bologna (Italy), Palermo (Italy), Ribeirão Preto (Brazil).

Suzanne Gage, a psychologist and epidemiologist at the University of Liverpool, in an accompanying commentary with the study said, "What this paper has done that's really nice is they look at rates of psychosis and cannabis use in lots of different places where underlying rates of psychosis are different".

  • Ismael Montgomery