Under U.S. law since 1970, marijuana has been a Schedule I controlled substance. This means that the drug has no approved medical use. Twenty states and the District of Columbia have legalized marijuana for medical use even though it hasn’t been approved by the Food and Drug Administration (FDA) to be a medicine. There are a few reasons why it hasn’t been approved. There haven’t been enough studies to show that its benefits outweigh its harms—that is, that it doesn’t cause more problems than it treats. Also, because it is a plant, there is no way to know how much or exactly what chemicals a person is getting each time they use it (unlike with a pill or shot).
That said, there are medications containing synthetic (man-made)THC, the main active ingredient in marijuana, that are used to treat nausea in cancer patients undergoing chemotherapy, and to stimulate appetite in patients with wasting syndrome—severe, involuntary weight loss—due to AIDS.
Since the discovery of the cannabinoid system—receptors in the body that bind THC, and chemicals that act as these receptors—scientists are actively looking for ways to use this system for medical purposes. Several promising compounds are being tested for the treatment of obesity, pain, and other disorders. However, it is unlikely that smoked marijuana will be developed as a medication because of its negative health effects.