Many people use marijuana for medical purposes - and even more claim they do- but it is actually only approved for a limited number of treatments. The Food and Drug Administration approved a drug called dronabinol, which is made from the cannabis plant, commonly known as marijuana, to treat cancer patients' nausea and vomiting in 1985. Since then, research on other medical uses of cannabis has been sparse because of the recreational stigma attached to the drug, but patients might also benefit from its pain-relieving properties. Researchers from Denmark jumped into the debate, testing dronabinol on patients with multiple sclerosis.

What the researchers wanted to know: Does dronabinol reduce pain in people with multiple sclerosis?

What they did: The researchers gave half the participants dronabinol every day for three weeks, while half received a placebo. At the end of that period, the patients waited three weeks with no treatment, then the groups switched. All of the participants kept a diary to record the intensity of their pain and general feelings throughout the study. The patients continued taking their regular MS medications during the trial, but stopped taking most pain killers.

What they found: For most of the participants, dronabinol reduced their pain significantly. On average, the patients reported a 1-point drop in pain on a scale of 1 to 10 when they were on the drug, and no drop in pain when they were on the placebo. However, dronabinol also caused some negative side effects, the most common being dizziness, headaches, or fatigue, causing some patients to reduce their doses.

What it means to you: Cannabis-based drugs may be promising as a type of pain relief because they appear to be effective, with few severe side effects. Still, this isn't a try-it-at-home treatment, so talk to your doctor about what could work for you–and keep you on the right side of the law.

Caveats: This study was done with only 24 subjects who reported on their own pain levels. Two thirds of them guessed accurately when they were taking the drug and when they were on the placebo, so their expectations may have contributed to their self-reported reduction in pain.

Find out more: The National Cancer Institute has a page on using marijuana to treat cancer patients.

The people who run the website the Science of Medical Marijuana are—no surprise—in favor of medical marijuana. Their website lists a few reports and studies.

Read the article: Svendsen, K.B., Jensen, T.S., Bach, F.W. "Does the Cannabinoid Dronabinol Reduce Central Pain in Multiple Sclerosis? Randomised Double Blind Placebo-Controlled Crossover Trial". British Medical Journal. July 31 2004, Vol. 329, No.7460, pp. 253-257

Abstract online: http://bmj.bmjjournals.com