In recent years, cannabis has become much stronger than it used to be.
Back in the early 2000s, most dried cannabis in Canada contained about 4% THC, the main chemical that causes the ‘high.’ But by 2025, that number has jumped to around 20% in most legal products.
This fivefold increase in THC strength is believed to play a big role in the rising number of people experiencing psychosis and even schizophrenia after using cannabis.
Dr. Nicholas Fabiano, a medical doctor and researcher in psychiatry at the University of Ottawa, emphasized this point, saying, ‘Cannabis from the 2000s is not the same as in 2025. THC content has increased by 5 times. This is likely a significant driver in the increasing link between cannabis use and schizophrenia.’
Scientific studies now clearly show that using high-strength cannabis regularly—especially products with more than 10% THC—raises the risk of psychosis. This risk is even higher for people who are young, male, or have a history of mental health conditions like depression or anxiety.
One massive study from Ontario looked at data from 9.8 million people. It found that individuals who went to the emergency room for cannabis use were 14 times more likely to later be diagnosed with a schizophrenia-related disorder.
Even more alarming, people who had cannabis-induced psychosis had a 241 times higher risk of developing schizophrenia-spectrum disorders.
Experts warn that continuing to use cannabis after having psychotic symptoms can make the condition worse. The best way to treat cannabis-induced psychosis is to stop using the drug and take antipsychotic medication. For people with severe or long-lasting symptoms, medication is often necessary.
Therapies like motivational interviewing and cognitive behavioral therapy can also help people quit cannabis and stick to their treatment plans. These approaches, provided by doctors or psychologists, teach strategies to avoid cravings and make healthier decisions.
As cannabis continues to evolve in strength and availability, it is crucial to understand the risks involved—especially for young people and those with mental health histories. High-potency cannabis might seem harmless, but it can have serious, long-lasting effects on brain health.
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 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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