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).

Current users who said they intended to quit cannabis reported greater psychosis-like experiences (OR, 1.131; 95% CI, 1.044-1.225; P less than 0.003). People who expressed a desire to continue, meanwhile, reported increased pleasurable experiences (OR, 0.892; 95% CI, 0.814-0.978; P less than 0.015).

The differences remained statistically significant across groups when age, sex, frequency of use, age of first use, and other drug use were accounted for.

“What we’re showing is that, if you have these psychotic experiences, you stop using,” Dr. Sami said. “And even if you continue using, you’re more likely to say you’re going to stop using in the future.”

Dr. Sami noted that nearly 40% of survey respondents reported having been treated for, or sought treatment for, a mental health complaint but cautioned against assuming these were attributable to cannabis use. “It’s very difficult to tease out whether they were using cannabis to self-medicate,” he said.

The new findings could help guide clinicians whose patients express a desire to quit and report psychosis-like experiences associated with cannabis. Helping patients elucidate those experiences could help inform conversations about risk and plans to quit, he said.

Currently, “we don’t really treat people who have these kind of experiences. If you came to me, as a psychiatrist, and asked me why I’m getting paranoid when I use cannabis, I’d tell you to stop using cannabis,” he said.

“But people who continue to use cannabis have a higher risk of psychotic disorder. And we’re now finding out that people who have psychotic-like experiences when they use cannabis tend to be more likely to develop psychotic disorders. So if I smoke weed and I start hearing voices and become suspicious, it might be a marker for me to develop schizophrenia.”

Dr. Sami and his colleagues are continuing to examine, by way of an online survey, why people might have very different experiences with the same drug. The survey is open to all adults whether they use cannabis or not at thecannabissurvey.com.

The research group declared support from the U.K. National Institute for Health Research, King’s College London, the Medical Research Council, and the U.K. Society for the Study of Addiction. The researchers reported no financial conflicts of interest.

SOURCE: Sami MB et al. Psychol Med. 2018 Mar 23. doi: 10.1017/S0033291718000569.

Cannabis users at highest psychosis risk may elect to quit