It's now legal to use marijuana to treat certain medical conditions in 25 states, but the Food and Drug Administration has still not approved the marijuana plant as a treatment for any disease or health issue. That's because there haven't been enough large studies of the drug to show that its benefits outweigh the risks in patients who use it, said the National Institute on Drug Abuse (NIDA). And in order to gain approval, researchers also need show that marijuana is safer or more effective than existing treatments for certain conditions.
Nevertheless, scientists have good reason to think that the marijuana plant could be useful in treating a number of medical conditions. The active ingredient in marijuana, delta-9-tetrahydrocannabinol (THC), has been shown to increases appetite and reduces nausea. Another chemical in marijuana, cannabidiol (CBD), may decrease pain and inflammation and help with muscle-control problems, according to NIDA. Both THC and CBD belong to a group of chemicals called cannabinoids.
Live Science has rounded up the promising evidence that medical marijuana may help people with certain conditions. Here's what we found:
Nausea and vomiting in cancer patients
Cancer patients who undergo chemotherapy may develop nausea and vomiting as a side effect of their treatment. A 2015 analysis of three studies involving cancer patients undergoing chemotherapy found that nausea and vomiting completely stopped in 47 percent of patients using cannabinoids (THC or CBD), while the symptoms completely stopped in only about 20 percent of those who took a placebo. Another study, of 15 cancer patients who both took THC orally and smoked marijuana, found that most patients experienced reduced nausea and vomiting, compared to when they didn't receive these drugs.
Another study, of 600 cancer patients, found that the compound nabilone (a synthetic form of THC) was better at preventing nausea and vomiting than were several existing anti-nausea medications. However, more studies are needed to determine whether smoking marijuana works better than newer types of anti-nausea medications for this purpose, a 2016 review said.
Pain in patients with multiple sclerosis
Marijuana may reduce feelings of burning, tingling or numbness, as well as pain from muscle spasms, in patients with multiple sclerosis (MS), according to a 2014 review study. The study found strong evidence that oral cannabis extract, which is a pill made from CBD, or a combination of THC and CBD, can help with these symptoms, the researchers said. However, not enough studies have been conducted to determine whether smoking marijuana helps with symptoms of MS, the review found.
Chronic pain in patients with cancer
A small study of 36 cancer patients found that 10 milligrams of THC produced pain-relieving effects comparable to those of taking 60 mg of the opiate codeine. Another study of a drug called nabiximols (brand name Sativex), which is a "marijuana mouth spray" that contains both THC and CBD, found that low and medium doses of the spray had better pain-relieving effects than a placebo. This result was found in cancer patients with pain who had not been helped by taking opioid drugs. However, very few studies have looked at the benefits of smoked marijuana for treating pain in cancer patients.
A 2010 study looked at 23 patients who had neuropathic pain (which is pain caused by damage to nerves) after trauma or surgery. The study found that those who smoked marijuana reported they had less pain and slept better than those who were given a placebo. A 2013 study of 39 people found that vaporized cannabis reduced neuropathic pain in patients who had not been helped by other treatments.
A 2015 study examined whether a daily dose of cannabis extract could help people with severe epilepsy who had not been helped by previous treatments. The study included 137 people who ranged in age from toddlers to adults. It found that the number of seizures that participants experienced declined by 54 percent over a 12-week period. Still, the study did not include a "control group" of participants who didn't take the drug, so it's not clear if the results were due to a placebo effect, the researchers said.
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Rachael is a Live Science contributor, and was a former channel editor and senior writer for Live Science between 2010 and 2022. She has a master's degree in journalism from New York University's Science, Health and Environmental Reporting Program. She also holds a B.S. in molecular biology and an M.S. in biology from the University of California, San Diego. Her work has appeared in Scienceline, The Washington Post and Scientific American.