A new review of nearly 100 studies has found that cannabis products with high levels of THC—the chemical that causes the “high”—are linked to several mental health problems, including psychosis, schizophrenia, and cannabis use disorder.
The review, published in the journal Annals of Internal Medicine, was done by researchers at the University of Colorado Anschutz Medical Campus and other institutions. They analyzed 99 studies involving over 221,000 people conducted between 1977 and 2023.
Cannabis products come in many forms, and some now have much higher levels of THC than in the past. This review focused on products with THC levels over 5 milligrams per serving or over 10% concentration. It also included forms like “shatter,” “dabs,” and other concentrates known for their high potency.
The researchers looked at how these products affect mental health. They grouped effects into three types: short-term (within 12 hours), medium-term (after one to two months of regular use), and long-term (after more than a year of regular use).
The mental health issues they studied included anxiety, depression, psychosis, schizophrenia, and problems with addiction, especially cannabis use disorder.
The results showed a strong link between high-THC cannabis and serious mental health issues. In studies that didn’t test cannabis for medical purposes, high-THC products were often associated with psychosis, schizophrenia, and addiction to cannabis.
In fact, none of the studies testing medical use showed any benefit for people with psychosis or schizophrenia.
When it came to anxiety and depression, the results were mixed. About half of the medical studies showed that high-THC products might help with anxiety and depression, but others showed harm. In non-medical studies, more than half reported worse anxiety, and about 4 in 10 showed worse depression.
Overall, the review supports earlier research that warned about the risks of high-THC cannabis. The more THC there is, the more likely a person is to experience negative mental health effects.
However, the researchers also noted that the current evidence still has many gaps. The studies included in the review were not all designed the same way, and many had limitations that make it hard to give definite answers.
The researchers say there is a need for better studies in the future. They want to see research that looks more closely at how different THC levels affect different people over time. This would help doctors and the public get clearer guidance about the risks and possible benefits of cannabis use.
In summary, while some people may use cannabis to try to relieve symptoms of anxiety or depression, this review highlights that high-THC products may do more harm than good for many people—especially when it comes to serious mental illnesses like psychosis and schizophrenia.
More research is needed, but for now, caution is advised when using high-potency cannabis products.
If you care about mental health, please read studies about 6 foods you can eat to improve mental health, and B vitamins could help prevent depression and anxiety.
For more health information, please see recent studies about how dairy foods may influence depression risk, and results showing Omega-3 fats may help reduce depression.
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