Teen Cannabis Use Skyrockets Psychotic Disorder Risk

Teen cannabis use dramatically raises the risk of developing psychotic disorders by 11 times, posing a serious health threat according to a new Canadian study.

Teen Cannabis Use

Teen Cannabis Use Dramatically Raises Risk of Psychotic Disorders

Using cannabis significantly increases the risk of teenagers developing a psychotic disorder. A Canadian study discovered that teens who use cannabis are 11 times more likely to develop such disorders compared to non-users. This risk is much higher than previous studies indicated. A 2016 analysis of data from ten different studies showed that heavy cannabis users were about four times more likely than non-users to be diagnosed with schizophrenia or another psychotic condition.

Key Findings of the Study

  • Increased Potency of Cannabis: Since the 1970s and 80s, the concentration of THC (tetrahydrocannabinol), the main active ingredient in cannabis, has risen significantly. Estimates suggest an increase of 14 to 19 percent as of 2017-2018.
  • High-Potency Varieties: A study of 1,560 UK adults found that high-potency varieties of cannabis have been linked to higher rates of psychosis. Using stronger strains as a teen doubles the risk of a psychotic episode.
  • Focus on Formal Diagnoses: The new study focused on formal diagnoses of psychotic disorders, such as schizophrenia, rather than acute psychotic episodes or symptoms. This approach provided a clearer picture of the long-term impact of teen cannabis use.

Detailed Study Insights

Study Approach:Researchers from McMaster University, led by epidemiologist André McDonald, analyzed data on cannabis use among teens and young adults collected between 2009 and 2012. They linked this survey data with public health records in Ontario, Canada, up to 2018. This allowed them to track recorded diagnoses of psychotic disorders, such as schizophrenia, among approximately 11,300 individuals.

Findings:The researchers discovered a strong association between cannabis use and the risk of adolescents being diagnosed with a psychotic disorder. Teens aged 12-19 who used cannabis had 11 times higher diagnosis rates compared to non-users. However, this association did not extend into young adulthood (ages 20 to 33) in this particular Canadian study.

Neurodevelopmental Theory

The findings align with the neurodevelopmental theory suggesting that teens are especially vulnerable to the effects of cannabis because their brains are still developing. Prior to this study, little epidemiologic evidence supported this view.

Challenges in Determining Causation

Most psychotic disorders begin to develop in late adolescence and early adulthood. It’s challenging to determine if this development is linked to cannabis use, underlying genetics, trauma experiences, or a combination of these factors. The study did not include genetic factors or trauma history, making it impossible to definitively state that teen cannabis use caused the recorded psychotic disorders. Observational studies like this can only point to associations.

Real-World Implications

The team found that 5 in 6 teens who presented to an emergency department or were hospitalized in Ontario for a psychotic disorder had previously reported cannabis use. This data suggests a strong link between cannabis use and psychotic disorders in teens.

Policy Changes and Future Analyses

Canada legalized the recreational use of cannabis in 2018, the final year of health data included in this study. Future analyses may reveal how these policy changes have affected adolescent health.

Broader Perspective on Psychotic Episodes

A recent meta-analysis found that around 1 in 200 cannabis users (0.5 percent) may experience psychosis, which involves hallucinations, delusions, and paranoia, even if only temporarily.

Key Takeaways

  • Teen cannabis use significantly increases the risk of developing psychotic disorders.
  • The potency of cannabis has increased over the decades, contributing to higher risks.
  • Formal diagnoses provide a clearer understanding of long-term impacts.
  • Teens are particularly vulnerable to cannabis’s effects due to brain development.
  • Future studies may reveal more about the impact of cannabis legalization on adolescent health.


  • “These findings are consistent with the neurodevelopmental theory that teens are especially vulnerable to the effects of cannabis,” says McDonald.
  • “The vast majority of teens who use cannabis will not develop a psychotic disorder, but most teens diagnosed with a psychotic disorder likely have a history of cannabis use,” McDonald explains.


Q: How much more likely are teens who use cannabis to develop psychotic disorders?A: Teens who use cannabis are 11 times more likely to develop psychotic disorders compared to non-users.

Q: Does the risk extend into young adulthood?A: In this particular study, the increased risk did not extend into young adulthood (ages 20-33).

Q: Why are teens more vulnerable to the effects of cannabis?A: Teens’ brains are still developing, making them more susceptible to the negative impacts of cannabis.

Q: How has the potency of cannabis changed over the years?A: The concentration of THC in cannabis has risen by between 14 and 19 percent since the 1970s and 80s.

Q: What percentage of cannabis users may experience psychosis?A: Around 1 in 200 cannabis users (0.5 percent) may experience psychosis.

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