Cannabis users at highest psychosis risk may elect to quit

Cannabis users who experience symptoms suggestive of psychosis are more likely to stop using the drug – or report wanting to stop – than are those who report more pleasurable experiences.

This finding, published March 23 in Psychological Medicine, might help explain an epidemiological conundrum related to cannabis use.

Observational studies have linked cannabis use to psychosis incidence and have identified a dose-dependent increase in risk. Studies also have suggested that people who report cannabis-induced psychosis-like experiences, including hallucinations or paranoia, might be more prone to developing a psychotic illness if they continue to use cannabis.

Yet, despite evidence of increasing cannabis potency and cannabis use over the last 15 years, levels of psychotic disorders, such as schizophrenia, “are stable and have remained stable over time,” said Musa Basseer Sami, MD, the study’s lead author, in an interview. “This is a big stumbling block for anyone who says pot is associated with psychosis.”

Dr. Sami’s findings suggest that people who report psychosis-like experiences with cannabis might be those most likely to stop consuming it, in turn reducing their risk. “If people are discontinuing after bad experiences, and if such experiences are a risk factor for developing a psychotic disorder, they may be deselecting themselves” out of the cannabis-using population, said Dr. Sami of King’s College London.

For their research, the investigators conducted a cross-sectional online survey study of more than 1,200 current or previous cannabis users, about three-quarters of whom reported current use. To do this, they modified a validated survey tool called the Cannabis Experiences Questionnaire, which measures the euphoric and paranoid-dysphoric effects of cannabis. They also collected qualitative data from respondents explaining how their experiences shaped their attitudes on whether to continue using.

Having quit cannabis was associated with having greater psychosis-like experiences, Dr. Sami and his colleagues found (odds ratio, 1.262; 95% confidence interval, 1.179-1.351; P less than 0.001), while continued cannabis users were more likely to report pleasurable experiences (OR, 0.717; 95% CI, 0.662-0.776; P less than 0.001).