Cannabis May Worsen Mental Health Disorders, Major Study Reveals

A comprehensive new study has cast doubt on the effectiveness of medicinal cannabis in treating mental health and substance use disorders, despite their growing popularity for such conditions.

Researchers at the University of Sydney conducted an extensive review of 54 randomized controlled trials spanning from 1980 to 2025, analyzing the effects of cannabinoids as primary treatments for various mental health conditions. The study, published in The Lancet Psychiatry, included data from 2,477 participants, predominantly male (69%), with an average age of 33.

The findings challenge common prescribing practices in the United States, United Kingdom, and Australia, where depression, anxiety, and PTSD rank among the leading reasons for cannabis prescriptions. According to the researchers, there is “no evidence to suggest they are effective in treating these conditions.”

The analysis determined that cannabis-based treatments are “rarely justified” for routine mental health treatment, with the risk of adverse side effects approximately 75% higher than with alternative treatments. Lead study author Dr. Jack Wilson warned that “the routine use of medicinal cannabis could be doing more harm than good by worsening mental health outcomes,” citing increased risks of psychotic symptoms, cannabis use disorder development, and delays in accessing more effective treatments.

While some limited positive results emerged for treating cannabis use disorder, insomnia, Tourette’s symptoms, and certain autistic traits, the researchers classified this evidence as low quality. The study found no significant benefits for anxiety disorders, psychotic disorders, PTSD, opioid use disorder, or anorexia nervosa.

For several conditions, including ADHD, bipolar disorder, OCD, and tobacco use disorder, researchers determined there was insufficient data to draw meaningful conclusions. Notably, no randomized trials for depression met the review criteria, despite it being a common reason for medicinal cannabis prescriptions.

Dr. Thea Gallagher, clinical associate professor in the department of psychiatry at NYU Grossman School of Medicine, who was not involved in the research, highlighted the significance of this study compared to previous research. “Prior work frequently relied on self-reported symptoms or observational data, which can’t establish causation,” Gallagher explained. “Earlier studies often used synthetic cannabinoids or low-THC formulations that don’t reflect today’s real-world products.”

The researchers did acknowledge legitimate medical uses for cannabis, including reducing epileptic seizures, alleviating multiple sclerosis symptoms, and managing certain types of pain. However, they stressed that mental health conditions appear not to be among the appropriate applications based on current evidence.

Mental health professionals recommend that cannabis users should carefully monitor changes in their psychological well-being, including mood, motivation, sleep patterns, anxiety levels, concentration ability, and social engagement. Dr. Gallagher advised watching for warning signs such as needing increasingly higher doses, using cannabis primarily as a stress coping mechanism, experiencing paranoia, or feeling mentally foggy.

Dr. Jessica Watrous, clinical psychologist and chief clinical officer at Modern Health in California, pointed to accessibility issues in mental healthcare as a factor driving people toward cannabis. “Mental health care in our country can be expensive, hard to navigate and difficult to access… so it’s not necessarily surprising that people are looking for more immediate, easier-to-access ways to manage how they’re feeling,” she noted.

The study did have limitations, with researchers acknowledging that nearly half (44%) of the examined studies were considered high risk for bias due to flaws in design or reporting. Additionally, the reviewed studies encompassed varied product types, dosages, treatment durations, and patient groups, complicating interpretation of the results.

Dr. Gallagher also noted that “clinical trial conditions differ from real-world use, where people often consume higher doses, with more frequency, and sometimes alongside alcohol or nicotine,” suggesting the actual effects could differ in real-world settings.

As cannabis legalization expands worldwide and more people turn to cannabinoid products for mental health concerns, this comprehensive review provides critical context for patients, healthcare providers, and policymakers considering cannabis as a treatment option for psychiatric conditions.