Can cannabis use cause schizophrenia? Short answer, no. Well, Canada legalized recreational cannabis in 2018, and experts wondered how it might affect people living with mental health conditions, like schizophrenia. Would legalization lead to higher cannabis use among those already at increased risk for anxiety, depression, or psychosis?
Canada published a large National study of drug use in the Lancet Regional Health (read the actual study). The study collected data of self reporting drug use. The study provides answers to those questions. Or does it provide more questions?
The International Cannabis Policy Study
The study used six waves of the International Cannabis Policy Study (ICPS), this repeat cross-sectional analysis examined whether cannabis use changed from pre-legalization (2018) to five years post-legalization (2023) depending on mental health status. The study collected responses over several years, more than 92,000 Canadians between the ages of 16 and 65. It was fortunate that the data collection began one year before legalization and continued for five years afterward, because the study offers one of the clearest pictures yet of how use patterns evolved over time pre and post legalization. The goals were to see whether cannabis use changed over time — and whether those changes differed depending on a person’s mental health status.
One important finding stood out right away: across every year studied, cannabis use was consistently higher among people who reported experiencing a mental health condition. Individuals with anxiety, depression, bipolar disorder, post-traumatic stress disorder (PTSD), or schizophrenia were about twice as likely to report using cannabis in the past year compared to those without these conditions.
For instance, in 2023, about 64% of people reporting bipolar disorder said they had used cannabis in the past year, compared with roughly 28% of those reporting no recent mental health problems.
Pre-legalization vs. Post-legalization
So what happened after legalization?
In Canada, there was a difference from pre-legalization vs. post-legalization. Overall, cannabis use increased modestly in the year immediately following legalization — especially among people without a reported mental health condition. Past-year and daily use rose from 2018 to 2019 in this group and then generally stabilized.
Among people with anxiety and depression, past-year cannabis use also increased slightly right after legalization. However, there was no sustained long-term rise in daily or past-year use over the five years that followed.
For those reporting bipolar disorder, PTSD, or schizophrenia, researchers found no consistent pre- vs. post-legalization increase in cannabis use.
In other words, concerns that legalization would dramatically increase cannabis use among people with mental health conditions were not supported by this study — at least during the first five years.
What did the study actually show?
Anyways, what did the Canadian study actually show? The study highlighted an important reality: people experiencing mental health challenges were already using cannabis at significantly higher rates than the general population. Researchers note that some individuals may use cannabis to manage symptoms such as anxiety or sadness, even though long-term outcomes can be complex and sometimes negative. Cannabis use rates jumped in all mental health categories post-legalization compared to pre-legalization, (see the study for yourself).
As cannabis policy continues to advance, these findings remind us that legalization alone doesn’t appear to drive major increases among vulnerable groups — but the relationship between cannabis and mental health remains worthy of continued attention. The U. S. has their own national study (See our article).