Limited evidence for medicinal cannabis in most mental health conditions

A systematic review and meta-analysis found little evidence that cannabinoids improve outcomes for common conditions such as anxiety, post-traumatic stress disorder (PTSD) and other psychiatric disorders.

Medicinal cannabis is increasingly prescribed in Australia for mental health conditions. Between 2016 and 2022, a third (33.9%) of medicinal cannabis Special Access Scheme Category B applications were for psychiatric conditions. But new evidence suggests the clinical benefits for many of these indications remain uncertain.

A systematic review and meta-analysis published in The Lancet Psychiatry found no evidence that cannabinoids improve outcomes for common conditions such as anxiety, PTSD and other psychiatric disorders.

The findings come amid rapid growth in prescribing. More than one million approvals for medicinal cannabis products have been issued in Australia in recent years, and sales have tripled over the past 4 years.

Lead author Dr Jack Wilson from The Matilda Centre for Research in Mental Health and Substance Use (University of Sydney) said the findings highlight the gap between clinical use and the available evidence.

‘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.

Evidence exists for only a small number of conditions

The review analysed 54 randomised controlled trials involving 2,477 participants conducted between 1980 and 2025.

Across these studies, cannabinoids showed some benefit for a limited number of conditions. However, the certainty of evidence was generally low.

Signals of benefit were identified for:

• cannabis use disorder, where mixed cannabidiol (CBD) and delta-9-tetrahydrocannabinol (THC) products reduced withdrawal symptoms and cannabis use
• insomnia, where cannabinoids increased total sleep time in some trials
• tic or Tourette’s syndrome, where cannabinoids reduced tic severity
• autism spectrum disorder, where some studies reported reductions in autistic traits.

But these are signals only. Dr Wilson said these findings should be interpreted cautiously.

‘The overall quality of evidence for these other conditions, such as autism and insomnia, was low,’ he said.

No evidence of benefit for several commonly treated conditions

The review found no significant benefit for many of the mental health conditions for which medicinal cannabis is frequently prescribed.

These included anxiety disorders, PTSD, psychotic disorders, opioid use disorder, cocaine use disorder, obsessive-compulsive disorder, anorexia nervosa, bipolar disorder, ADHD and tobacco use disorder.

Researchers also found no randomised controlled trials assessing cannabinoids for the treatment of depression, despite this being a common indication for medicinal cannabis use.

In some cases, cannabinoids were associated with negative outcomes. For example, they increased cocaine craving among people with cocaine use disorder.

The authors concluded that routine use of cannabinoids for most mental health conditions is rarely justified based on the current evidence.

Safety signals and quality concerns

The review also identified limitations across the evidence base.

Nearly half of the included trials were assessed as having a high risk of bias and many involved small sample sizes or short treatment periods.

Cannabinoids were associated with higher rates of adverse events compared with placebo, including dizziness, nausea and dry mouth.

Overall, one additional patient experienced an adverse event for every seven people treated with cannabinoids.

Serious adverse events were not significantly increased in the trials. However, most studies examined regulated cannabinoid medicines rather than the higher THC products commonly used in clinical practice.

Implications for Australians using medicinal cannabis

The findings are particularly relevant in Australia, where medicinal cannabis prescribing continues to expand.

More than 700,000 Australians report using medicinal cannabis for more than 250 health conditions.

The rapid expansion of use of medicinal cannabis in Australia has previously been identified by PSA as problematic. In August last year, former PSA National President Associate Professor Fei Sim said the increasing availability of medicinal cannabis products presents challenges for clinicians and pharmacists.

‘Unregistered medicinal cannabis products pose serious challenges, including inconsistent dosing, limited safety data and minimal post-market surveillance,’ she said.

A/Prof Sim said current regulatory pathways were not intended for widespread routine prescribing.

‘The Special Access Scheme and Authorised Prescriber pathways were designed for unique clinical situations, not as a loophole for hundreds of products to bypass regulatory scrutiny,’ she said.

This has serious implications for pharmacists supporting patients using these products.

‘The current system leaves pharmacists and prescribers without the tools they need to ensure safe and informed use,’ A/Prof Sim said.

PSA supports the use of medicinal cannabis when clinically appropriate and overseen by qualified health professionals but this must be based on appropriate evidence and oversight.

‘There is a place for medicinal cannabis products, but we need to prioritise the tools and regulatory environment that promote their safe and appropriate use,’ she said.

Don’t miss the upcoming feature on medicinal cannabis prescribing in the June 2026 issue of AP.