Main papers published in lancet Studies have reported that medicinal cannabis does not effectively treat anxiety, depression, or post-traumatic stress disorder (PTSD). This analysis is the largest to date examining both the safety and effectiveness of cannabinoids in a wide range of mental health conditions.
These findings come at a time when the use of cannabis for medical purposes is widespread. Approximately 27% of 16- to 65-year-olds in the United States and Canada report using cannabis for medical purposes, and about half of them say they use cannabis to manage mental health symptoms.
Lead author Dr Jack Wilson, from the Matilda Center at the University of Sydney, said the results raised serious questions about the approval of medical cannabis for conditions such as anxiety, depression and PTSD.
“Although our paper does not specifically address this, routine use of medical cannabis may do more harm than good by worsening mental health outcomes, for example by increasing the risk of developing psychotic symptoms and cannabis use disorder, and by delaying the use of more effective treatments,” he said.
Limited evidence for other conditions
Researchers have found some signs that medical marijuana may be helpful in certain cases. These include cannabis use disorder (also known as cannabis dependence), autism, insomnia, and tics or Tourette syndrome.
However, Dr. Wilson stressed that the evidence supporting these uses is not strong.
“However, the overall quality of evidence for other conditions such as autism and insomnia was lower. Without robust medical and counseling support, the use of medical cannabis in these cases is rarely justified.
“However, while there is evidence that medical cannabis may be beneficial for certain health conditions, such as reducing seizures associated with some types of epilepsy, spasticity in people with multiple sclerosis, and managing certain types of pain, our study shows that there is insufficient evidence for mental health disorders.
“For autism in particular, this study showed some evidence that medicinal cannabis may help reduce symptoms, but it’s worth noting that the experience of autism is not universally or universally present, so this finding should be treated with caution.”
Results for substance use disorders are mixed.
This review also considers how medical cannabis affects various substance use disorders. Results varied by condition.
Cannabis-based treatments have shown potential to help people addicted to cannabis. However, this study found a worrying effect of increased craving with cannabis use in people with cocaine use disorder.
“Medical cannabis can be part of an effective treatment for people with cannabis use disorder, similar to how methadone is used to treat opioid use disorder. Oral formulations of cannabis have been shown to reduce cannabis smoking when administered alongside psychotherapy,” Dr. Wilson said.
“However, when medical cannabis was used to treat people with cocaine use disorder, their cravings increased. This means medical cannabis should not be considered for this purpose and may actually worsen cocaine dependence,” he said.
Call for stronger regulations on medical cannabis
The rapid increase in medical marijuana use and prescription is causing concern among major medical organizations, including the American Medical Association. Experts say there is limited regulation and continued uncertainty about how effective and safe these products actually are.
“Our study provides a comprehensive and independent assessment of the benefits and risks of cannabis medicines, which may help clinicians make evidence-based decisions and help ensure patients receive effective treatment while minimizing harm from ineffective or unsafe cannabis products,” Dr. Wilson said.
45 years of extensive global analysis
The findings are based on a systematic review and meta-analysis of 54 randomized controlled trials (RCTs) conducted around the world over a 45-year period (1980-2025).
This research was funded by NHMRC. Wayne Hall and Myfanwy Graham have received consulting fees from the World Health Organization. Wayne Hall received compensation for his expert testimony regarding the risks of cannabis use. Myfanwy Graham is a suitable member of the Australian Department of Health, Aging and Disability’s Medical Cannabis Expert Working Group. Mifanwy Graham has also received funding from the Therapeutic Goods Administration for an independent evidence review on medical cannabis. All other authors declare no competing interests.
