Major cannabis study finds little proof for popular medical claims, flags big dangers
A JAMA analysis of more than 2,500 studies over 15 years finds limited benefits for most medical uses and highlights safety risks, especially for youth and daily users.
A major analysis published in JAMA found little robust evidence to support most medical uses of cannabis and cannabinoids, while also flagging safety concerns. The review examined more than 2,500 scientific papers from the past 15 years, including randomized trials, other reviews, and clinical guidelines, to assess how strong the evidence is and to offer guidance for clinicians.
Led by researchers at UCLA Health Sciences with contributions from Harvard, UCSF, Washington University School of Medicine and New York University, the study set out to determine the clinical value of medical cannabis and cannabinoids. It is described as a narrative review rather than a systematic one, meaning it did not apply standardized methods to minimize bias in selecting and evaluating studies. It also notes that some evidence comes from observational research and may not establish cause and effect. The goal is to help clinicians weigh benefits against risks when discussing cannabis with patients.
The strongest evidence supports FDA-approved cannabinoid medications for certain conditions: HIV/AIDS-related appetite loss, chemotherapy-induced nausea and vomiting, and some severe pediatric seizure disorders.
For many other conditions commonly treated with cannabis — such as chronic pain, insomnia, anxiety or post-traumatic stress disorder — randomized trials have not shown meaningful benefits.
Safety concerns include that high-potency cannabis use among young people may be linked to higher rates of mental health issues. Daily inhaled cannabis use has been associated with increased risks of coronary heart disease, heart attack and stroke when compared with non-daily use.
Dr. Michael Hsu, a physician at UCLA Health Sciences and lead author of the review, said: "Patients deserve honest conversations about what the science does and doesn't tell us about medical cannabis." He noted that the study is a narrative review and that its limitations should be considered in clinical decision-making.
The authors urge clinicians to screen patients for cardiovascular risk, evaluate mental health history, check for potential drug interactions and consider conditions where risks may outweigh benefits. They encourage open, realistic conversations and caution against assuming cannabis is broadly effective for medical conditions.
The review also notes that some evidence comes from observational research rather than randomized trials, so causation cannot be established. The results may not apply to all populations, products or doses.
As cannabis remains widely used, clinicians are urged to weigh potential benefits against known risks and to communicate clearly with patients about what the science does and does not show.
