Huge study finds no evidence cannabis helps anxiety, depression, or PTSD

These findings arrive at a time when cannabis use for medical purposes is widespread. About 27 percent of people aged 16-65 in the United States and Canada report using cannabis medically, and roughly half of them say they use it to manage mental health symptoms.

Lead author Dr. Jack Wilson from the University of Sydney’s Matilda Centre said the results raise serious questions about approving medicinal cannabis for conditions like anxiety, depression, and PTSD.

“Though our paper didn’t specifically look at this, the routine use of medicinal cannabis could be doing more harm than good by worsening mental health outcomes, for example a greater risk of psychotic symptoms and developing cannabis use disorder, and delaying the use of more effective treatments,” he said.

Limited Evidence for Other Conditions

The researchers did find some indications that medicinal cannabis might help in certain cases. These include cannabis use disorder (otherwise known as cannabis dependency), autism, insomnia, and tics or Tourette’s syndrome.

However, Dr. Wilson emphasized that the supporting evidence for these uses is not strong.

“But the overall quality of evidence for these other conditions, such as autism and insomnia, was low. In the absence of robust medical or counseling support, the use of medicinal cannabis in these cases are 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.”

Mixed Results for Substance Use Disorders

The review also looked at how medicinal cannabis affects different substance use disorders. Results varied depending on the condition.

Cannabis-based treatments showed some potential for helping people with cannabis dependence. However, the study found a concerning effect in people with cocaine-use disorder, where cannabis use increased cravings.

“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.

Calls for Stronger Regulation of Medicinal Cannabis

The rapid rise in medicinal cannabis use and prescribing has raised concerns among major medical organizations, including the American Medical Association. Experts point to limited regulation and ongoing uncertainty about how effective and safe these products really are.

“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,” Dr. Wilson said.

Large Global Analysis Spanning 45 Years

The findings are based on a systematic review and meta-analysis of 54 randomized controlled trials (RCTs) conducted worldwide over a 45 year period (1980-2025).

The research was funded by the NHMRC. Wayne Hall and Myfanwy Graham have received consultation fees from the World Health Organization. Wayne Hall has received payment for expert testimony on the risks of cannabis use. Myfanwy Graham is an appropriate member of the Medicinal Cannabis Expert Working Group, Australian Department of Health, Ageing and Disability. Myfanwy Graham has also received funding from the Therapeutic Goods Administration for independent evidence reviews on medicinal cannabis. All other authors declare no competing interests.