Largest review finds no mental health benefits of medicinal cannabis

A landmark Lancet Psychiatry paper published today – the largest-ever review of the safety and efficacy of cannabinoids across a range of mental health conditions – found no evidence that medicinal cannabis is effective in treating anxiety, depression or post-traumatic stress disorder (PTSD). 

The study comes amid more than one million prescription approvals and a tripling of sales of cannabinoid medications (including both cannabidiol (CBD) and tetrahydrocannabinol (THC) products) in Australia over the past four years, often for the treatment of mental health and substance-use disorders. 

The study's lead author, Dr Jack Wilson at the University of Sydney's The Matilda Centre, said the results call into question the approval of medicinal cannabis for the treatment of depression, anxiety 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."

Dr. Jack Wilson, University of Sydney's The Matilda Centre

More than 700,000 Australians have reported using medicinal cannabis to treat over 250 different health conditions. The research found evidence to suggest that medicinal cannabis could potentially be beneficial for some conditions – such as the treatment of cannabis use disorder (otherwise known as cannabis dependency), autism, insomnia, and tics or Tourette's syndrome. 

Dr Wilson said: "But the overall quality of evidence for these other conditions, such as autism and insomnia, was low. In the absence of robust medical or counselling 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." 

The study found that medicinal cannabis was not effective for every type of substance-abuse disorder. While medicinal cannabis may help with cannabis dependence, it was found to increase cocaine cravings among people with cocaine-use disorder 

"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. 

Researchers urge greater regulation for prescribing of medicinal cannabis 

The rapid expansion in medicinal cannabis use and prescribing rates has raised concerns among major medical bodies, including the Australian Medical Association (AMA) and the Pharmacy Guild of Australia, about the largely unregulated growth in prescribing and the uncertainty surrounding the efficacy and safety of these products. 

In response, the Therapeutic Goods Administration (TGA) initiated a review of the regulatory oversight of medicinal cannabis, with more than 500 responses published in February. 

"Our study provides a comprehensive and independent assessment of the benefits and risks of cannabis medicines, which may support the TGA and 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. 

The systematic review and meta-analysis included results from 54 randomised controlled trials (RCTs) published over a 45-year period (1980-2025) worldwide.