Adolescents using cannabis are 11 times more likely to develop a psychotic disorder compared to adolescents who don’t use the drug. The corresponding study was published in Psychological Medicine.
Epidemiologic research suggests that youth cannabis use is linked to the development of psychotic disorders such as schizophrenia. However, how much such research applies today may be questionable as it relies heavily on data from the 20th century when cannabis was significantly less potent; the average THC potency of cannabis in Canada was around 1% in 1980 and 20% in 2018.
In the current study, researchers compared Canadian population-based survey data from 2009 to 2012 with healthcare data until 2018 to investigate the link between youth cannabis use and psychotic disorders. They included data from 11, 363 respondents aged 12-24 years old who had no prior psychotic disorder at baseline.
Ultimately, the researchers found that cannabis use during adolescence-but not young adulthood- was linked to 11 times higher rates of developing psychotic disorders. They further found that around 5 in 6 adolescents who had been hospitalized or who visited the emergency department for a psychotic disorder had previously reported cannabis use.
"We found a very strong association between cannabis use and risk of psychotic disorder in adolescence. Surprisingly, we didn’t find evidence of association in young adulthood. These findings are consistent with the neurodevelopmental theory that teens are especially vulnerable to the effects of cannabis,” said lead author André McDonald Ph.D., who conducted the study at ICES as part of his PhD at the University of Toronto, in a press release.
“Canadian youth are among the heaviest users of cannabis in the world. If we follow the precautionary principle, the bottom line is that more needs to be done to prevent early cannabis use,” Dr. McDonald added.
While the study points towards a correlation, it does not reveal causation. The researchers noted that it is possible that adolescents with psychotic symptoms were self-medicating with cannabis before receiving a diagnosis. They also noted that they did not account for factors like genetics and trauma history.
Sources: EurekAlert, Psychological Medicine