Studies find medical marijuana unproven to help many illnesses

• Evidence was weak that marijuana helps anxiety and sleep disorders
• Many edible products list inaccurate amounts of active ingredients

Medical marijuana has not been proven to work for many illnesses that state laws have approved it for, according to the first comprehensive analysis of research on its potential benefits.

The strongest evidence is for chronic pain and for muscle stiffness in multiple sclerosis, according to the review, which evaluated 79 studies involving more than 6,000 patients. Evidence was weak for many other conditions, including anxiety, sleep disorders, and Tourette's syndrome and the authors recommend more research.