Sparse Evidence for Cannabis to Treat Mental Health Conditions Highlights Research Gap

A sweeping review of cannabis studies over the past 45 years concludes there is little to no high-quality evidence showing cannabis is effective for treating mental health conditions. The findings, published in the medical journal The Lancet Psychiatry, underscore the extent to which the public's embrace of cannabis has outpaced the scientific research.

The new analysis represents the largest effort yet to systematically parse all the data from randomized-controlled trials on cannabis and mental health. A team of researchers in Australia looked at more than 50 clinical trials, considering a wide range of conditions, formulations, and types of cannabinoids.

The analysis turned up no evidence that cannabis can help with symptoms of anxiety, post-traumatic stress disorder, or depression - the psychiatric conditions that medical marijuana users most often mention when asked why they're taking the drug. Insomnia, autism, and tic or Tourette's syndrome had more supporting data, though even that evidence was deemed "low quality" by the authors.

"We clearly need to do more research on cannabis medicines," says Jack Wilson, a postdoctoral research fellow at the Matilda Centre for Research in Mental Health and Substance Use at the University of Sydney who led the review. "In the absence of evidence at this time, the routine use of medical cannabis products really should be rarely justified for the treatment of mental health disorders."

The findings are not altogether surprising for cannabis researchers who know first-hand how challenging it is to conduct and fund well-controlled trials. For more than 50 years, cannabis has been listed as a Schedule 1 drug by the Drug Enforcement Administration, though President Trump recently signaled he'd like the federal government to loosen that designation.

The study also warns of "substantial risks" in vulnerable groups, including adolescents and young adults, those at risk of substance use disorders, as well as people with bipolar disorder or psychotic disorders. There is a well-documented link between cannabis use at a young age and an increased risk of psychosis.

Experts emphasize that cannabis is not one thing because it's such a complex substance, and that high THC-containing products like gummies and concentrates, especially for those who have a serious mental illness, appear to carry the most risks.