The nation's largest physicians organization, with about 250,000 member doctors, the AMA has maintained since 1997 that marijuana should remain a Schedule I controlled substance, the most restrictive category, which also includes heroin and LSD.
In changing its policy, the group said its goal was to clear the way to conduct clinical research, develop cannabis-based medicines and devise alternative ways to deliver the drug.
"Despite more than 30 years of clinical research, only a small number of randomized, controlled trials have been conducted on smoked cannabis," said Dr. Edward Langston, an AMA board member, noting that the limited number of studies was "insufficient to satisfy the current standards for a prescription drug product."
The decision by the organization's delegates at a meeting in Houston marks another step in the evolving view of marijuana, which an AMA report notes was once linked by the federal government to homicidal mania. Since California voters approved the use of medical marijuana in 1996, marijuana has moved steadily into the cultural mainstream spurred by the growing awareness that it can have beneficial effects for some chronically ill people.