Researchers assess rates of cannabis-associated psychotic episodes

A team of computational biologists and psychologists from University College London, working with a colleague from the University of Lausanne, has attempted to estimate how often and what types of marijuana users experience a psychotic episode due to their smoking habits.

In their study, published in the journal Nature Mental Health, the group analyzed prior research efforts to learn more about the frequency of psychotic episodes among marijuana users and what they learned by doing so.

Anecdotal evidence and some research efforts have found that marijuana smokers can experience a psychotic episode as a result of inhaling smoke from burning marijuana. As the researchers on this new effort note, little research has addressed this phenomenon, including why it occurs, which type of smokers experience episodes, and how often.

A psychotic episode is a state in which a person experiences difficulties perceiving reality. Such episodes can include delusions, hallucinations and difficulty discerning what is real and what is not. Psychotic episodes are sometimes associated with mental illness, and may also occur when people take certain substances, such as those found in marijuana. For marijuana users, psychotic episodes can last from a few hours to an entire day.

To learn more about such episodes in marijuana smokers, the research team obtained and analyzed papers from 162 studies involving approximately 200,000 volunteer smokers to learn more about its impact on the body.

The researchers found that overall, just 0.5% of marijuana users included in the studies experienced a "severe" psychotic episode. But they also found that the likelihood of an episode varied widely depending on the circumstances surrounding its use. They found, for example, rates of 19 to 21% in observational studies, but just 2% in medicinal studies.

They also found no genetic link, or any increased risk for frequent users, though heavy users did appear to have a higher risk. They also found that young people were slightly more susceptible, as were female smokers.

The research team concludes that not all people who smoke marijuana have an equal risk of experiencing a psychotic episode and that the likelihood of having such an experience varies depending on the circumstances in which the marijuana is inhaled.

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