Despite the rising popularity of medical cannabis for mental health and addiction, a new sweeping review shows little proof that these products actually help treat most of these conditions. The comprehensive analysis reveals that while cannabis-based medicines might offer mild relief for a handful of specific issues, they do not improve conditions like depression or anxiety and carry a greater risk of side effects. These findings were recently published in the journal The Lancet Psychiatry.
Cannabinoids are the active chemical compounds found in the cannabis plant. The most well-known of these are tetrahydrocannabinol, which produces the high associated with marijuana, and cannabidiol, a non-intoxicating compound often sold as a wellness product. In recent years, an increasing number of people have turned to these substances to manage their mental health.
In the United States and Canada, roughly 27 percent of people between the ages of 16 and 65 report using cannabis for medical reasons. About half of those individuals use it specifically to treat mental health struggles. In Australia, prescription approvals for cannabinoid medications have soared, often for psychological conditions and addiction.
This surge in use has largely outpaced the medical evidence. Researchers wanted to know if prescribing these plant-based and pharmaceutical products was truly justified based on science. Jack Wilson, a researcher at the University of Sydney in Australia, led a team to investigate whether these treatments actually work and whether they are safe.
The research team sought to provide clarity during a time of expanding clinical use. They noticed a substantial gap between how often these products are prescribed and the scientific proof backing them up. To bridge this gap, Wilson and his colleagues set out to gather and evaluate all the best available data from the past four decades.
To figure out if cannabinoids are effective, the researchers conducted a systematic review and meta-analysis. A systematic review involves searching through major scientific databases to collect every study that meets a strict set of criteria. A meta-analysis then combines the numerical data from all those separate studies into one large statistical model.
Combining data this way allows researchers to see the big picture. It gives them a much clearer idea of a treatment’s true effect than looking at any single study alone. For this project, the team searched for randomized controlled trials published between January 1980 and May 2025.
A randomized controlled trial is considered the highest standard of scientific research for testing medical treatments. In these studies, participants are randomly assigned to either receive the treatment being tested or a placebo. A placebo is an inactive substance, like a sugar pill, that looks just like the real medication but has no physical effect.
The researchers ultimately gathered 54 of these trials, which included a total of 2,477 participants. They looked specifically for trials where a mental health condition or a substance use disorder was the primary reason for treatment. They evaluated how well the cannabinoids reduced symptoms and tracked any adverse events, which are unwanted side effects like dizziness or nausea.
The results for most mental health conditions were not statistically significant. The data showed no true benefit for people struggling with anxiety, psychotic disorders, or post-traumatic stress disorder. There were also no randomized trials available that tested cannabis as a primary treatment for depression.
This absence of proof is particularly notable because anxiety, depression, and post-traumatic stress disorder are among the most common reasons people seek out medical cannabis. The researchers found the same lack of benefit for obsessive-compulsive disorder and bipolar disorder. In trials testing treatments for attention-deficit hyperactivity disorder, the improvements were not statistically significant.
For eating disorders, the findings were similarly unsupportive. Two studies looked at people with anorexia nervosa, an eating disorder characterized by an intense fear of gaining weight. The researchers found no real difference in weight gain or physical activity levels between those who took cannabinoids and those who received a placebo.
The team also looked at substance use disorders, which occur when a person cannot stop using a drug or medication despite it causing health and social problems. They found no benefit for treating opioid addiction or tobacco dependence. In fact, for people with a cocaine use disorder, the results showed that taking cannabinoids actually increased their cravings for cocaine.
Wilson noted this specific danger in a recent statement about the research. He cautioned against applying one drug to all addictions. “However, when medicinal cannabis was used to treat people with cocaine-use disorder, it increased their cravings. This means it should not be considered for this purpose and may, in fact, worsen cocaine dependence,” he said.
The analysis did find a few areas where cannabinoids offered some potential benefits, though the quality of the evidence was generally considered low. One such area was the treatment of cannabis use disorder itself. People with this condition struggle to control their use of marijuana.
The data showed that using pharmaceutical-grade combinations of tetrahydrocannabinol and cannabidiol helped reduce withdrawal symptoms and the total amount of cannabis a person consumed. Wilson likened this to other addiction treatments. “Similar to how methadone is used to treat opioid-use disorder, cannabis medicines may form part of an effective treatment for those with a cannabis-use disorder. When administered alongside psychological therapy, an oral formulation of cannabis was shown to reduce cannabis smoking,” he said.
Another area showing slight improvement was the treatment of tic disorders and Tourette’s syndrome. These conditions cause sudden, uncontrollable movements or vocal sounds. Participants who received a combination of tetrahydrocannabinol and cannabidiol experienced a reduction in the severity of their tics compared to those who took a placebo.
The researchers also looked at autism spectrum disorder, a developmental condition that affects how people communicate and interact with the world. Across two studies, cannabinoids were linked to a reduction in certain traits associated with autism. However, the researchers cautioned that these specific studies had a high risk of bias, meaning the way the trials were designed or reported might have skewed the results.
Sleep issues were another condition where cannabinoids showed some promise. Among people with insomnia, taking any type of cannabinoid led to an increase in total sleep time. This was measured both by electronic sleep-tracking devices and by the participants writing in sleep diaries.
Despite these few positive notes, the safety data raised some concerns. Participants who took cannabinoids were more likely to experience general adverse events than those in the placebo groups. For every seven people treated with these medicines, one additional person experienced a side effect like dry mouth, nausea, or diarrhea.
The researchers noted that the medications did not increase the odds of serious adverse events. Serious adverse events are severe medical issues that might require hospitalization or pose a major health threat. People taking cannabinoids were also no more likely to drop out of the studies than those taking a placebo.
Even with a relatively mild side effect profile, Wilson warned about the broader implications of these findings. He noted that unproven treatments carry hidden risks. “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.
There are a few caveats to consider when interpreting these results. The studies included in the review were often quite small, which makes it harder to draw firm conclusions. The researchers also pointed out that many of the trials had a high risk of bias, often because the companies manufacturing the cannabis products were involved in funding or running the studies.
Additionally, the review only looked at outcomes from the longest follow-up period in each study. This means they might have missed some short-term benefits or harms that occurred earlier in the treatment process. The analysis was also limited by a lack of data on whether these treatments affect men and women differently.
Moving forward, the researchers emphasized the need for better-designed studies. Future trials must include larger groups of participants to provide clearer, more accurate results. Scientists also need to conduct studies that are free from industry influence to ensure the findings are completely independent.
Until that better evidence arrives, the researchers urge medical professionals to be highly cautious. They hope their work guides safer prescribing practices. “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,” Wilson said.
The study, “The efficacy and safety of cannabinoids for the treatment of mental disorders and substance use disorders: a systematic review and meta-analysis,” was authored by Jack Wilson, Olivia Dobson, Andrew Langcake, Palkesh Mishra, Zachary Bryant, Janni Leung, Danielle Dawson, Myfanwy Graham, Maree Teesson, Tom P Freeman, Wayne Hall, Gary C K Chan, and Emily Stockings.
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