Daily Use of High-THC Cannabis Linked to Increased Risk of Mental Disorders

For quite some time, scientists and medical professionals have been interested in the potential risk of developing various psychological disorders associated with regular use of psychoactive cannabis strains. Recently, a team of researchers from the UK attempted to answer this question by analyzing the personal histories of 901 patients diagnosed with different forms of psychosis living in EU countries and Brazil. The results, published in the latest issue of the medical journal Lancet, indicate a certain correlation between regular use of high-THC cannabis and the onset of psychosis. However, the authors also note that this correlation does not prove that psychoactive cannabinoids directly cause such disorders when the plant is used frequently.

Is There a Link Between Frequent Cannabis Use and Psychosis?

For many years, medical professionals have tried to establish a connection between regular recreational cannabis use and the development of various psychological disorders. Throughout the last century, authorities in different countries have used such studies as justification for strict criminalization of cannabis. Despite attempts to link these studies and their findings to addiction or increased risk of psychological illness, research has consistently shown that a wide range of complex, interrelated factors may influence the development of such phenomena. The new study follows similar conclusions.

So, what did the British researchers discover during their experiment? Data was collected from 2010 to 2015 in 11 cities across Europe and Brazil. The researchers interviewed 901 people who had been diagnosed with psychosis within a year prior to the survey. After analyzing the data and adjusting for possible external factors, the responses of these patients were compared to those of a control group of 1,237 volunteers who had never used cannabis. The statistics showed that, on average, people who regularly used high-THC cannabis were indeed more likely to develop psychosis and other mental disorders than those who did not use cannabis.

“We found that the risk of developing psychosis among cannabis users was, on average, 5% higher than among people who do not use the plant recreationally,” the study notes.

It’s important to mention that the study does not clearly define “high-THC cannabis.” While the authors specify that they are referring to plant material rather than extracts, they generally classified any cannabis strain containing more than 10% THC among its active compounds as “high-THC,” which aligns with the UK’s formal definition of “skunk” cannabis. In other words, by this definition, nearly every modern recreational cannabis strain—whether legal or from the black market—would be considered high-THC.

Although the authors do not directly blame cannabis for causing psychosis, they do suggest that restrictions on cannabis distribution “could significantly reduce the risk of such disorders among the population.” On the other hand, the study acknowledges that the average risk level and types of mental disorders observed varied significantly between this research and 11 other similar studies conducted over the past decade.

Opposing Views: Cannabis as Self-Medication for Psychosis Symptoms

As critics of the new study quickly pointed out, “the presence of a correlation between cannabis use and psychosis does not mean that cannabis use is the cause of these conditions or their progression.” In fact, the lead researcher, Dr. Marta Di Forti, admitted in an interview that the risk of developing psychosis as a result of regular cannabis use is only a “potential consequence,” not a scientifically established pattern.

One critic, Dr. Suzanne Gage, a professor of psychology and epidemiology at the University of Liverpool, suggested that the study’s authors may have misinterpreted the data. She noted that the researchers did not consider the possibility of reverse correlation between psychosis and frequent cannabis use. The researchers assumed that cannabis use increases the risk of psychosis, as is the prevailing opinion among medical experts, without considering that people prone to mental disorders might use cannabis as a form of self-medication for their symptoms.

Despite the tendency among medical professionals to believe that cannabis may increase the risk of psychological disorders, it’s important to remember that scientists have not yet identified the mechanisms by which cannabinoids could negatively affect brain function.

Regarding the survey itself, it’s worth noting that Dr. Di Forti and her colleagues only asked patients about their cannabis use prior to the onset of psychological symptoms. They did not determine how long participants had been using cannabis before their diagnosis, nor did they ask about their personal reasons for using cannabis. This leaves open the possibility that many participants may have used cannabis for self-medication.

In any case, while the authors acknowledge the possibility of errors and inaccuracies in their data analysis, they also urge medical professionals to continue researching the link between cannabis use and the development of psychosis to confirm or refute this hypothesis. In particular, beyond simple surveys of cannabis users with psychological disorders, scientists should focus on the biological mechanisms by which cannabinoids affect the nervous system and brain to determine possible neurophysiological bases for the risk of psychosis.