People who use cannabis every day may be at increased risk for psychotic disorder, especially if they use a high-potency form of the drug, according to a 2019 study in Lancet Psychiatry. The risk is especially concerning because cannabis has been legalized or decriminalized in many countries, potentially making its use more common.
Researchers from 11 sites across Europe collected data from 2010 to 2015 on 901 people who had experienced a single episode of psychosis, in which people lose contact with reality, and 1,237 people who had not experienced psychosis. The study revealed that people who reported using cannabis on a daily basis had more than triple the odds of psychotic disorder compared with those who never used cannabis. Those who used a high-THC form of the drug every day had nearly five times the odds. (THC is the chemical responsible for most of marijuana’s psychological effects).
One weakness of the study is that participants reported their own use of cannabis, which is a less reliable way to obtain data than using an objective measure such as a blood test. Also, the study does not prove that daily cannabis use causes psychosis; it only shows an association. It’s possible that people predisposed to psychosis may be self-medicating with cannabis.
Although the medicinal properties of cannabis are being increasingly appreciated, people who decide to use it need to be aware of its adverse effects, especially with frequent or high-potency use.