Dozens of clinical trials have tested medical marijuana for 10 conditions. A comprehensive review of those trials by an international team of researchers found little reliable evidence that the drug does what it is purported to do. The report was published in the Journal of the American Medical Association (JAMA).
The researchers analyzed studies that tested marijuana against placebos (fake pills), usual care, or no care. The JAMA researchers considered over 25 studies involving almost 2,500 patients and concluded that there was moderate- quality evidence that marijuana reduced cancer pain and chronic neuropathic pain by modest amounts. However, marijuana was not effective in relieving pain of fibromyalgia, HIV-associated pain, rheumatoid arthritis, and multiple sclerosis. The researchers reviewed 79 studies with over 6,000 patients and found moderate-quality evidence that medical marijuana was helpful in treating muscle spasticity in people with multiple sclerosis. There was no conclusive evidence that marijuana was effective in treating depression, anxiety disorder, psychosis, or reducing eye pressure in glaucoma. The study also showed that medical marijuana users were at much greater risk for adverse side effects such as dizziness, dry mouth, sleepiness, confusion, and more serious problems such as liver, kidney, and psychiatric disorders.
It is possible that marijuana could have wide-spread benefits, the researchers say, but there are no high-quality studies to show this. They recommend more research.