By Zachary Stieber

There is no evidence medical cannabis works against anxiety, depression, or post-traumatic stress disorder, according to a new study.

Researchers with the University of Sydney and other institutions undertook a review of available evidence and ended up analyzing 54 randomized, controlled trials that were conducted from 1980 to 2025.

“There were no significant effects on outcomes associated with anxiety, anorexia nervosa, psychotic disorders, post-traumatic stress disorder, and opioid use disorder,” they wrote in the paper, which was published on March 16 by The Lancet.

The authors also said there was an absence of evidence from randomized, controlled trials for using cannabinoids, a form of medical cannabis, to treat depression.

An earlier review, published in 2025, said there was scant evidence medical cannabis works against a variety of conditions, such as insomnia. Medical cannabis is approved in a number of countries for different purposes. In the United States, where it is approved for dealing with issues such as seizures, President Donald Trump has directed officials to reclassify cannabis from a schedule I narcotic to a schedule III to allow medical research.

Researchers behind the new paper said that they found signs that medical cannabis can help with symptoms such as insomnia and disorders such as autism.

“But the overall quality of evidence for these other conditions, such as autism and insomnia, was low,” Jack Wilson, a postdoctoral research fellow at the University of Sydney and one of the researchers, said in a statement. “In the absence of robust medical or counseling support, the use of medicinal cannabis in these cases are rarely justified.

“Our study provides a comprehensive and independent assessment of the benefits and risks of cannabis medicines, which may support clinicians to make evidence-based decisions, helping to ensure patients receive effective treatments while minimising harm from ineffective or unsafe cannabis products,” Wilson added.

The authors said they believe the paper is the largest and most comprehensive systematic review and meta-analysis on randomized, controlled trial evidence for medical cannabis against mental disorders and substance use disorders. They said that new randomized-controlled trials should be run that feature “larger and more representative samples.”

Limitations included largely being unable to analyze differences based on gender or sex, because that information was absent from most of the trials.

Funding came from the National Health and Medical Research Council and other sources. Conflicts of interest included payments for several authors from the World Health Organization. One author reported receiving money for expert testimony on cannabis risks.