Cannabis-based medicines have shown little evidence of effectiveness for treating most mental health and substance-use disorders, according to a large review of past studies published in a major medical journal on Monday.

Medical use of cannabinoids has been expanding, including in the United States, Canada and Australia, where many patients report using cannabis products to manage conditions such as anxiety, post-traumatic stress disorder and sleep problems.

Researchers reviewed data from 54 randomized clinical trials conducted between 1980 and May 2025 involving 2,477 participants for their analysis published in The Lancet. The studies assessed cannabinoids as a primary treatment for mental disorders or substance-use disorders.

Overall, the review found no significant benefit for several conditions commonly cited as reasons for medical cannabis use, including anxiety disorders, psychotic disorders, PTSD and opioid-use disorder.

"Some people may experience legitimate benefits, and that's great. But when we look at the evidence as a whole, we just don't see that the evidence is quite there for the routine use of these medicines," said lead author Jack Wilson from the University of Sydney's The Matilda Centre.

The study authors found no randomized controlled trials evaluating cannabinoids for depression, highlighting a major gap in the evidence base, they noted.

Limited evidence suggested potential benefits for certain conditions.

A combination of cannabidiol, commonly known as CBD, and THC - the substance that causes a high from marijuana - was associated with reduced cannabis withdrawal symptoms and lower cannabis consumption among people with cannabis-use disorder.

Cannabinoids were also linked to reductions in tic severity in people with Tourette's syndrome.

Researchers also found a reduction in some autistic traits in those with autism spectrum disorder, and increased sleep time in patients with insomnia among those treated with cannabis medicines. But the overall quality of evidence for autism and insomnia was low, said Wilson.

The researchers said more high-quality trials with larger and more representative samples are needed to clarify the therapeutic role of cannabinoids, particularly as their clinical use grows.

"We clearly need to do more research on medical cannabis, particularly for those conditions that have limited alternative treatments," Wilson said.

-Reporting by Sriparna Roy in Bengaluru; Editing by Bill Berkrot/Reuterss