Cannabis may backfire for mental health disorders, major study finds

A large body of research found there is little strong evidence that medicinal cannabinoids help with mental disorders and substance-use disorders.

Researchers at the University of Sydney, Australia, reviewed 54 randomized controlled trials, from 1980 to 2025, where cannabinoids (the active substances found in cannabis) were used as the primary treatment.

Most of the 2,477 participants were male (69%) and averaged 33 years old. The paper was published in The Lancet Psychiatry.

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The researchers noted that depression, anxiety and PTSD are some of the leading reasons that cannabis products are prescribed in the U.S., U.K. and Australia, but that there is "no evidence to suggest they are effective in treating these conditions."

The analysis found that cannabis-based treatments are "rarely justified" for routine use, and that the risk of adverse side effects was about 75% higher.

A few results showed promise for treating cannabis use disorder, insomnia, Tourette’s symptoms and autistic traits, but the evidence was still low quality, the study found.

Cannabinoids did not show a significant benefit for anxiety disorders, psychotic disorders, PTSD, opioid use disorder or anorexia nervosa.

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The researchers did not find enough data to determine cannabis' effect on ADHD, bipolar disorder, OCD or tobacco use disorder, and no randomized trials for depression met the review criteria.

In a University of Sydney press release, lead study author Dr. Jack Wilson said these findings 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," he said.

The researchers did note, however, that medicinal cannabis was shown to be beneficial for certain health conditions, such as reducing epileptic seizures, multiple sclerosis symptoms and certain types of pain.

Dr. Thea Gallagher, clinical associate professor in the department of psychiatry at the NYU Grossman School of Medicine, compared this new research to prior studies that dealt with smaller sample sizes and shorter follow-up periods.

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"Prior work frequently relied on self-reported symptoms or observational data, which can’t establish causation," Gallagher, who was not involved in the study, told Fox News Digital. "Earlier studies often used synthetic cannabinoids or low-THC formulations that don’t reflect today’s real-world products."

"This new review is the most comprehensive attempt to date to evaluate cannabis specifically for anxiety, depression and PTSD."

Gallagher reiterated that cannabis does have legitimate medical uses, but that mental health conditions "are not necessarily among them at this time."

"Using cannabis to manage emotional distress may delay access to proven treatments," she cautioned. "People with a personal or family history of psychosis should be especially cautious."

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The mental health expert encouraged cannabis users to monitor changes in mood, motivation, sleep, anxiety, concentration and social engagement over time.

"Watch for red flags, such as needing higher doses, using cannabis to cope with stress, increased paranoia or feeling mentally ‘foggy,’" Gallagher advised, adding that people should "check in with trusted friends or family … and take periodic tolerance breaks to see whether cannabis is helping or masking underlying issues."

People should seek professional support if their mood or functioning begin to decline, she added.

Dr. Jessica Watrous, clinical psychologist and chief clinical officer at Modern Health in California, who was also not involved in the study, said it's important for people to recognize why they are turning to cannabis to manage mental health symptoms.

"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 told Fox News Digital.

"But what the authors of the paper call out is that by using a more immediately available, but less evidence-backed intervention, it may delay getting support that does have strong evidence of effectiveness."

Watrous urges people to prioritize their mental health just as they do their physical health. "You can do this by actively engaging in clinically proven mental health support, whether that’s therapy, coaching, meditation, or just working in small moments of self-care every day."

Almost half (44%) of the studies were considered high risk for bias, meaning flaws in how they were designed or reported may make their findings less reliable, the researchers noted.

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The studies also included a mix of product types, doses, durations and patient groups, making the results more difficult to interpret.

"Clinical trial conditions differ from real‑world use, where people often consume higher doses, with more frequency, and sometimes alongside alcohol or nicotine," Gallagher noted.