FILE - This Feb. 1, 2011 file photo shows medical marijuana clone plants at a medical marijuana dispensary in Oakland, Calif. Medical marijuana has not been proven to work for many of the illnesses state laws have approved it for, according to the first comprehensive analysis of research on its purported benefits published Tuesday, June 23, 2015 in the Journal of the American Medical Association. The strongest evidence of benefit is for chronic pain and for muscle stiffness in multiple sclerosis, according to the analysis, which analyzed 79 studies involving more than 6,000 patients. Evidence was weak for many other conditions, including nausea from chemotherapy, sleep disorders, HIV-related weight loss and Tourette syndrome. (AP Photo/Jeff Chiu, File)CHICAGO (AP) — 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.