Massachusetts voters in 2 weeks will consider becoming the 18th state to legalize the use of marijuana for medical purposes. Individual doctors and patient advocacy groups, including the AIDS Action Committee of Massachusetts and the state chapter of the Leukemia and Lymphoma Society, have endorsed the ballot question, saying marijuana can help patients and is available now. To study marijuana, researchers must be licensed by the US Drug Enforcement Administration and get access to marijuana grown at the University of Mississippi, which contracts with the National Institute on Drug Abuse to produce the only federally sanctioned supply. That process can prove onerous, if not impossible, acting as a deterrent for those who might want to study marijuana's benefits, some researchers said. In 2000, the University of California created the Center for Medicinal Cannabis Research, with $9 million from the state. Dr. Igor Grant, the center's director, ... and colleagues have completed the most comprehensive research to date of the effects of marijuana in patients, including studies that were randomized and double-blind, gold standards in research. Four studies found the drug to be useful in treating pain. Three were in patients with HIV who had pain resulting from damage to their nervous system. Another study found that marijuana reduced muscle stiffness in patients with multiple sclerosis.