How does medical marijuana affect the body?

Americans who doubt that marijuana has medicinal benefits are now — squarely — in the minority. According to a Healthday/Harris Poll released this July, nearly 9 in 10 Americans now support legalizing the drug for medicinal use (compared to just 57 percent for recreational). This sentiment is reflected in the nation's legal landscape, where 31 states (plus D.C., Guam, and Puerto Rico) have legalized it for medical use. But with a Schedule I classification remaining from the Drug Enforcement Administration, the drug remains federally illegal — making it difficult to track down information about its benefits and dangers. Part of this stems from researchers' inability to study the drug's effects on humans, since the DEA considers Schedule I substances as having "no currently accepted medical use." So how does medical marijuana work to treat various ailments in the body?