Preliminary clinical trials show marijuana might be useful for pain, nausea and weight loss in cancer and HIV/AIDS and for muscle spasms in multiple sclerosis. Medical marijuana studies in the U.S. are dwindling fast, however, as funding for research in California--the only state to support research on the whole cannabis plant--comes to an end this year and federal regulations on obtaining marijuana for study remain tight.

In July the Drug Enforcement Administration denied a petition, first filed in 2002 and supported by the American Medical Association, to change marijuana’s current classification. So marijuana remains in the administration’s most tightly controlled category, Schedule I, defined as drugs that “have a high potential for abuse” and “have no currently accepted medical use in treatment in the U.S.” Many medical cannabis proponents see a catch-22 in the U.S.’s marijuana control. One of the DEA’s reasons for keeping marijuana in Schedule I is that the drug does not have enough clinical trials showing its benefits. Yet the classification may limit research by making marijuana difficult for investigators to obtain.