A new review found that medicinal cannabis does not reduce symptoms in a range of conditions it is increasingly used to treat including substance use disorder, anxiety, and PTSD. The research was published in The Lancet Psychiatry.
As of 2018, an estimated 27% of people aged between 16 and 65 in the US and Canada reported using medical cannabis at some point in their lives, with significant numbers using the substance to manage mental health symptoms.
"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," said lead author of the study, Dr. Jack Wilson, Postdoctoral Research Fellow at the Faculty of Medicine and Health at the University of Sydney, Australia, in a press release.
For the study, the researchers conducted a systematic review and meta-analysis of 54 randomized controlled trials, including close to 2,500 participants, conducted all over the world between 1980 and 2025. The trials evaluated the efficacy of cannabinoids for reducing or treating various mental health disorders and substance use disorders. Participants had an average age of 33 years old.
Ultimately, the researchers found that cannabis had no significant effect on outcomes linked to anxiety, anorexia, psychotic disorders, PTSD, and opioid use disorder. Data was insufficient for ADHD, bipolar disorder, OCD, and tobacco use order, while there was an absence of data for treating depression.
They did find, however. that combination of cannabidiol and delta-9-tetrahydrocannabinol reduced tic severity among those with tic or Tourette’s Syndrome compared to placebo, and that taking cannabinoids led to a reduction in autistic traits among those with autistic spectrum disorder.
"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,” said Wilson.
Sources: Science Daily, The Lancet Psychiatry
