A Canadian study found that drug use increases a teenager’s risk for psychotic disorders by 11 times. This is a stronger association than previous studies have reported. A 2016 analysis of 10 different studies found that the heaviest cannabis users were four times more likely than non-users to be diagnosed with schizophrenia or another psychotic condition.
In addition to the age of drug users, most of the data used in previous analyzes of adolescent drug use are from before 2000, according to the team behind the new analysis.
Estimates vary, but from the 1970s and 80s, the concentration of THC (tetrahydrocannabinol), the main active ingredient in cannabis, increased between 14 and 19 percent between 2017 and 2018.
Earlier this year, a study of 1,560 adults in the UK found that high-potency forms of cannabis were associated with higher rates of psychosis, with use of a strong strain during adolescence doubling young adults’ risk for psychotic episodes.
In this new study, McMaster University epidemiologist Andre MacDonald and his colleagues looked at official diagnoses of psychotic disorders, such as schizophrenia, rather than acute psychotic episodes or psychotic symptoms.
They also analyzed psychoses in late adolescence and early adulthood to ensure that they do not miss a critical window (as other studies have) when psychotic disorders begin to appear.
The team linked survey data on adolescent and youth cannabis use collected between 2009 and 2012 to public health records in Ontario, Canada through 2018. This allowed them to track diagnoses of psychotic disorders such as schizophrenia. after the use of marijuana among 11,300 people.
Research has found a strong link between marijuana use and an adolescent’s risk of a psychotic disorder diagnosis. The rate of diagnosis was 11 times higher among adolescents aged 12 to 19 years who reported using marijuana.
However, this association was not found in the 20- to 33-year-old age group, at least in this Canadian study.
McDonald says “These findings are consistent with the neurodevelopmental theory that adolescents are more vulnerable to the effects of marijuana”.
Prior to this study, there was little epidemiological evidence to support this idea,” the team wrote in their paper.
Most psychotic disorders begin to appear in adolescence and early adulthood, but it doesn’t matter whether it’s related to the person using marijuana, or the person’s underlying genetics, traumatic experiences, or a combination of those factors.
MacDonald and colleagues’ analysis of health records and research data did not include genetic factors or a history of trauma, so it is unclear whether adolescent marijuana use causes documented psychotic disorders. Such observational studies, however large, can only point to associations.
But the team used those health records to find that 5 out of 6 teenagers who went to an emergency department or were treated in an Ontario hospital for a psychotic disorder reported using marijuana in the Canadian National Health Survey.
McDonald says “The majority of adolescents who use drugs will not develop a psychotic disorder, but according to these data, the majority of adolescents diagnosed with a psychotic disorder have a history of marijuana use”.
Canada legalized recreational marijuana use in 2018, the latest year for which health data is available, so future research may reveal how this policy change affects teen health.
Looking closer to a psychotic episode than a diagnosis, a recent meta-analysis found that more than 200 cannabis users (or only 0.5 percent) may have psychosis – a frightening experience that involves hallucinations, delusions, and paranoia, even if only temporarily.
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