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A major new analysis, the largest review of clinical trials on cannabis-based medicines, has found no evidence that medical cannabis is effective for treating depression, anxiety, or post-traumatic stress disorder (PTSD). The systematic review examined more than 50 randomised controlled trials and raises concerns about the widespread use and regulation of cannabinoid therapies for mental health conditions.

Medical cannabis use has been growing across the world. This is especially true in the United States, Canada, and Australia. It is being used for mental health conditions such as depression, anxiety, and PTSD.

University of Sydney researchers reviewed data from 54 randomised clinical trials conducted between 1980 and May 2025 involving 2,477 participants for their analysis, assessing the use of cannabinoids as a primary treatment for mental disorders or substance-use disorders.

“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.

A review found limited and generally low-quality evidence for cannabis-based treatments in mental health conditions. Modest benefits were seen for improved sleep, reduced tic severity, and easing cannabis withdrawal symptoms. There was no significant effect for anxiety, PTSD, or other major disorders. There was no evidence at all supporting its use for depression. The study also showed increased side effects and some risks. Higher cocaine cravings were seen in certain groups. This suggests cannabis is not a reliable or well-supported treatment for most mental health conditions.

“Similar to how methadone is used to treat opioid-use disorder, cannabis medicines may form part of an effective treatment for those with a cannabis-use disorder. When administered alongside psychological therapy, an oral formulation of cannabis was shown to reduce cannabis smoking,” Dr Wilson said.

“However, when medicinal cannabis was used to treat people with cocaine-use disorder, it increased their cravings. This means it should not be considered for this purpose and may, in fact, worsen cocaine dependence,” he said.

Dr Wilson continued: “But the overall quality of evidence for these other conditions, such as autism and insomnia, was low. Without robust medical or counselling support, using medicinal cannabis in these cases is rarely justified.”

“There is, however, evidence that medicinal cannabis may be beneficial in certain health conditions, such as reducing seizures associated with some forms of epilepsy, spasticity among those with multiple sclerosis, and managing certain types of pain, but our study shows the evidence for mental health disorders falls short.

“In the case of autism specifically, while the study showed some evidence medicinal cannabis could assist with a reduction in symptoms, it is worth noting that there is no one – or universal – experience of autism, so this finding should be treated with caution.”