Study finds few benefits from medical marijuana

The Lancet Psychiatry journal published a study on Monday that reported scarce evidence to support medicinal marijuana use for mental health. Scientists ultimately found mostly low-quality evidence supporting the use of medical marijuana as the primary treatment for mental and substance-abuse disorders, according to the abstract.

A group of scientists from the University of Sydney’s Matilda Centre for Research in Mental Health and Substance Use analyzed 45 years' worth of results from randomized controlled trials testing the effectiveness of medical marijuana use. The study, funded by the National Health and Medical Research Council, considered any cannabidiol, or any product containing THC or CBD, as medicinal marijuana. The research group described the study as the largest and most comprehensive systematic review and meta-analysis of evidence from trials from 1980 to 2025.

What were the study’s full results? The routine use of medical marijuana for treating mental disorders or substance issues is currently rarely justified, given the scarcity of evidence, the study concluded. Analysis found no benefit from medical marijuana in treating opioid abuse disorder, anxiety, psychotic disorders, PTSD, or anorexia nervosa, the study reported. The study found insufficient data to make any conclusions on medical marijuana’s effectiveness to treat ADHD, bipolar disorder, obsessive-compulsive disorder, or tobacco abuse disorder.

Scientists found some low-quality evidence that marijuana may help symptom reduction for cannabis abuse disorders, insomnia, Tourette’s syndrome, and autism, according to the journal. Cannabinoids were also linked to a greater risk of adverse events, but not serious events, the report added.

It’s concerning that patients may be using medical marijuana in place of more effective therapies, given that medical marijuana use increased based on the product’s low risk profile, not from evidence that it’s effective, according to the study. Marijuana products may include additional unidentified harms, since the randomized controlled trial outcomes analyzed did not record long-term harms, the study noted. There’s a serious need for more quality research and randomized controlled trials with larger samples, the group added.

The new study came several months after President Donald Trump reclassified marijuana as a controlled substance with legitimate medical uses. The president reported that those who struggle with chronic pain, including the elderly, cancer patients, and wounded soldiers, had been pushing for the redesignation for years.

Dig deeper: Read my report for more background on Trump reclassifying marijuana last December.