Cannabis today is very different from what it was 20 years ago.
According to Dr. Nicholas Fabiano, a researcher and medical doctor at the University of Ottawa’s Department of Psychiatry, the main ingredient in cannabis that causes the ‘high,’ known as THC, has increased in strength by about five times compared to cannabis from the early 2000s.
This big jump in potency is now believed to play a major role in the growing connection between cannabis use and serious mental health problems such as schizophrenia.
In Canada, THC levels in most legal dried cannabis have risen from about 4% in the early 2000s to around 20% today. Research shows that using cannabis with high THC levels, especially more than 10%, is linked to a greater risk of psychosis.
Psychosis is a serious mental health condition where people lose touch with reality, sometimes seeing or hearing things that are not there. The risk is even higher for those who use cannabis often, start using it at a younger age, or are male. People with a history of mental health problems, such as depression or anxiety, may also be more vulnerable.
A large study in Ontario looked at the health records of 9.8 million people. The researchers found that those who had to go to the emergency department for problems related to cannabis use were more than 14 times more likely to develop schizophrenia or related disorders compared to people who had not used cannabis.
The risk became even more extreme for people who experienced cannabis-induced psychosis, a severe reaction to the drug that can cause intense confusion, paranoia, and hallucinations. For these individuals, the chance of developing a schizophrenia-spectrum disorder was more than 240 times higher.
The study also showed that continuing to use cannabis after experiencing cannabis-induced psychosis can greatly increase the risk of the symptoms coming back. For treatment, doctors usually recommend stopping cannabis use completely and may prescribe antipsychotic medication for those with severe or ongoing symptoms.
Behavioral therapies such as motivational interviewing or cognitive behavioral therapy can also help. These approaches can teach people skills to manage cravings, avoid relapse, and follow treatment plans.
Cannabis use disorder, which means being unable to control cannabis use even when it causes problems, is another serious issue. People with this condition may find it harder to quit, even when their health is at risk. For them, getting professional help can make a big difference.
Experts point out that today’s cannabis is much stronger and potentially more dangerous than what previous generations used. This means that using it carries a greater risk of long-term mental health problems, especially for young people and those with a family history of mental illness.
While some people may believe cannabis is harmless or even helpful, this research shows that heavy use—particularly of high-THC strains—can have serious consequences.
In reviewing the findings, it becomes clear that the increase in THC content over the last two decades is not a small change—it is a dramatic one with real effects on public health. The link between high-potency cannabis and mental illness is becoming stronger in scientific evidence.
Public awareness, education, and careful regulation may be important steps to reduce harm, especially for vulnerable groups. This is not just about personal choice—it is also about understanding the risks that come with a drug that is far stronger than it used to be.
If you care about mental health, please read studies about One sleepless night can reverse depression for days and findings of Scientists find better treatment for older adults with depression.
For more information about mental health, please read studies about Frequent painkiller use linked to mental health risks in these people and findings of Common depression drugs may offer new treatment for bipolar disorder.
The study is published in CMAJ.
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