The Largest Review of Medical Cannabis for Mental Health Finds Little Evidence It Works

Medicinal cannabis has become increasingly popular for treating anxiety, depression and post-traumatic stress disorder (PTSD), but a major new review suggests the scientific evidence does not support its widespread use for these conditions. Researchers found little to no meaningful benefit, raising questions about the rapid expansion of cannabis prescribing and self-medication for mental health disorders.

The review, published in The Lancet, is described as the largest analysis to date examining the effects of cannabis-based medicines on mental health. According to the authors, current prescribing practices have moved well ahead of the available evidence.

Growing use despite limited evidence

In North America alone, around 27% of people aged 16–65 report using cannabis for medical purposes, with approximately half taking it to manage symptoms such as anxiety, depression, stress or trauma.

Lead author Dr. Jack Wilson from the University of Sydney's Matilda Centre said the evidence does not justify routine prescribing of medicinal cannabis for common mental health conditions. He also warned that relying on cannabis may delay access to treatments with proven effectiveness and, in some cases, could worsen existing psychiatric problems.

The review also highlights several potential risks associated with cannabis use, including an increased likelihood of psychotic symptoms, cannabis use disorder and cognitive impairment, particularly with long-term use or products containing high levels of THC. The researchers argue that these risks should be carefully weighed against the limited benefits identified.

Limited benefits in a few specific conditions

Although the overall findings were largely negative for anxiety, depression and PTSD, researchers did identify modest evidence of potential benefits in several more specific conditions.

These included reducing symptoms of cannabis use disorder itself, improving certain behavioral symptoms associated with autism spectrum disorder, enhancing sleep in people with insomnia and decreasing tic severity in individuals with Tourette syndrome.

However, the authors emphasize that the supporting evidence remains generally low in quality. Most clinical trials were relatively small, short in duration and used different cannabis formulations, doses and treatment protocols, making it difficult to draw reliable clinical conclusions.

They conclude that prescribing medicinal cannabis for these conditions outside structured medical or psychological care is rarely justified and call for larger, high-quality randomized controlled trials before broader recommendations can be made.

Better evidence for some neurological conditions

The review clearly distinguishes psychiatric conditions from neurological disorders where cannabis-based medicines have stronger scientific support.

Previous research has demonstrated benefits for certain standardized cannabinoid medications in treating rare forms of epilepsy, multiple sclerosis-related muscle spasticity and some types of chronic pain.

Even in these cases, however, regulatory agencies such as the U.S. Food and Drug Administration have approved only a limited number of carefully standardized cannabis-derived medicines.

The authors caution that many commercially available cannabis oils, edibles and vaping products differ substantially from the products evaluated in clinical trials. Variations in cannabinoid content, dosing and product quality make it difficult to predict either effectiveness or safety in real-world use.

Mixed results for addiction treatment

The researchers also examined cannabis-based treatments for substance use disorders.

For cannabis dependence, some studies found that an oral cannabis formulation combined with psychological therapy reduced withdrawal symptoms and helped decrease cannabis use. Researchers note that this approach has drawn comparisons with methadone treatment for opioid dependence, although considerably more evidence is needed before it could become standard clinical practice.

The findings were very different for cocaine use disorder. In those studies, medicinal cannabis actually increased cocaine cravings, leading the authors to conclude that it should not be used as a treatment for cocaine addiction.

Researchers call for stronger regulation

According to the authors, the rapid expansion of medicinal cannabis programs around the world has outpaced the scientific evidence supporting many approved uses. Medical organizations, including the American Medical Association, have previously expressed similar concerns about cannabis being promoted for conditions where convincing clinical evidence remains limited.

The review analyzed data from 54 randomized controlled trials conducted over approximately 45 years, providing one of the most comprehensive assessments of both the potential benefits and risks of medicinal cannabis.

Dr. Wilson said the goal of the review is to help clinicians make evidence-based decisions by distinguishing between conditions where cannabis-based medicines appear effective, where they do not, and where the evidence remains uncertain.

The researchers also disclosed funding sources and potential conflicts of interest, including advisory work for organizations such as the World Health Organization and government health agencies. They noted that most authors reported no competing interests and that the review underwent independent peer review.