High-potency marijuana use appears to be associated with an increased risk of a first psychotic episode, based on a case-control study conducted in Europe. “Daily users of a strong type of cannabis face a significant increase in the probability of developing a psychotic disorder,” reported Marta Di Forti, MD, PhD, MRC, lead author of a study whose preliminary results were presented at the International Congress on Schizophrenia Research. Dr. Di Forti spawned a media boomlet in 2015 when she and her colleagues raised the prospect of a possible association between so-called “skunk” marijuana and first psychotic episodes. In their study of subjects in London with first-time psychotic episodes and matched population controls, those who had psychotic episodes were three times (adjusted odds ratio: 2.92; 95% confidence interval, 1.52-3.45; P = .001) as likely as controls to have used “skunk” marijuana (Lancet Psychiatry. 2015 Mar;2:233-8).
In the new study, Dr. Di Forti and her colleagues analyzed 1,200 first-incident cases of psychosis that were captured between the years 2010 and 2013 by the European Network of National Schizophrenia Networks Studying Gene-Environment Interactions project (EU-GEI). The researchers compared the cases to 1,300 population-based controls in five unidentified European countries and found that daily users of high-potency marijuana had the highest adjusted odds ratio (4.5-8, statistical significance not available) of a psychotic episode (Schizophr Bull. 2017 Mar:43:S30. doi: 10.1093/schbul/sbx021.078). “This effect is significant even after controlling for other drugs of abuse such as stimulants, tobacco and alcohol, and main sociodemographic confounders,” the researchers wrote in their abstract.
“The biology of cannabis-associated psychosis is still unclear,” Dr. Di Forti said in an interview. “Nevertheless, we know that THC (tetrahydrocannabinol) binds with two receptors called CB1 and CB2. They’re part of the endocannabinoid system, which from uterus onward protects our central nervous systems from insults. It activates on demand if the brain goes on hypoxia or we experience a brain injury.”