The American Medical Association on Tuesday issued a cautious but historically significant call to change America's marijuana prohibition laws, urging a "review" of the drug's status as a Schedule I drug.

At a meeting in Houston, the AMA's House of Delegates adopted a new policy that calls for "marijuana's status as a federal Schedule I controlled substance be reviewed with the goal of facilitating the conduct of clinical research and development of cannabinoid-based medicines, and alternate delivery methods."

That does not mean the AMA supports the legalization or decriminalization of marijuana.

Schedule I drugs are those considered to have no medical benefit and to be harmful when used under any circumstances. As such, marijuana is currently grouped by the federal government with drugs like heroin and LSD. By comparison, cocaine and methamphetamines are classified as Schedule II drugs, which may have some clinical benefits when used in the proper circumstances. The AMA's stance could simply result in the rescheduling of marijuana as a controlled substance that has some medical benefit.

However, Aaron Houston, director of government relations for the Marijuana Policy Project, calls the move "historic" all the same, noting that it comes from "what has historically been America's most cautious and conservative major medical organization."

"Marijuana's Schedule I status is not just scientifically untenable, given the wealth of recent data showing it to be both safe and effective for chronic pain and other conditions, but it's been a major obstacle to needed research," he said in a statement.

"It's been 72 years since the AMA has officially recognized that marijuana has both already-demonstrated and future-promising medical utility," said medical student Sunil Aggarwal in a press statement from Americans for Safe Access. Aggarwal has been spearheading the effort by the AMA's youth wing to change the organization's attitude towards marijuana.

ASA government affairs director Caren Woodson pointed out that the American College of Physicians, the country's second-largest medical group, called for a review of marijuana's status last year.

"The two largest physician groups in the US have established medical marijuana as a health care issue that must be addressed," Woodson said. "Both organizations have underscored the need for change by placing patients above politics."

In its report (PDF), the AMA stated:

Results of short term controlled trials indicate that smoked cannabis reduces neuropathic pain, improves appetite and caloric intake especially in patients with reduced muscle mass, and may relieve spasticity and pain in patients with multiple sclerosis. However, the patchwork of state-based systems that have been established for .medical marijuana. is woefully inadequate in establishing even rudimentary safeguards that normally would be applied to the appropriate clinical use of psychoactive substances. The future of cannabinoid-based medicine lies in the rapidly evolving field of botanical drug substance development, as well as the design of molecules that target various aspects of the endocannabinoid system. To the extent that rescheduling marijuana out of Schedule I will benefit this effort, such a move can be supported.

The AMA's move is the latest in a series of small but significant shifts in attitudes towards the liberalization of marijuana policies.

Last month, conservative columnist George F. Will said that the US is "probably in the process" of legalizing marijuana, pointing to the Obama administration's new policy to no longer raid medical marijuana clinics that are legal under state law, so long as those state laws are being observed. (Though one California-based US attorney disputes that there has been any change in policy.)

Additionally, California is currently debating a proposal to decriminalize marijuana. Massachusetts decriminalized marijuana in a state ballot last year.

And recent polls show that support for decriminalization of marijuana has reached a record high in the United States, with some 44 percent of Americans now in favor of reducing or eliminating criminal penalties for possession of the herb.