Twenty states have legalized medical marijuana, and in many of these, just about any ailment earns you a card allowing you access to it. A big reason for this is that doctors and researchers still have little understanding of how to best use pot medically. "There are only two types of people in the world: Those who think that cannabis will cure everything, and those who think that cannabis will cure nothing," says Dr. J.H. Atkinson, professor of psychiatry at the University of California, San Diego. We offer a third kind of person: A handful of researchers who, in clinics around the country, conduct serious experiments on the potential benefits of this controversial drug. It's not surprising that the research is still quite preliminary. Marijuana's status as a Schedule I drug, the lack of government funding for research, and the existence of only one federal growing facility, in Mississippi, for all sanctioned medical marijuana research are just some of the major obstacles in the way of quality cannabis science. Even with this limited research, pot shows promise for some conditions, but not for others. We've outlined the facts about the better-known conditions.