CHICAGO — A big research analysis says medical marijuana has not been proven to work for many illnesses for which state laws have approved it.

The analysis found the strongest evidence is for chronic pain and for muscle stiffness in multiple sclerosis. But the authors say evidence is weak for many other conditions, including anxiety, sleep disorders, and Tourette's syndrome.

The analysis evaluated 79 studies involving more than 6,000 patients. It's published in Tuesday's Journal of the American Medical Association.

A separate study tested edible medical marijuana products and found many labels don't accurately list amounts of the active ingredients. More than half had lower than listed amounts but some had higher than listed amounts.