Marijuana advocates who hoped the cascade of states moving to legalize medical marijuana would soften the federal stance on the drug faced disappointment Thursday as the Drug Enforcement Administration announced it will keep marijuana illegal for any purpose.



Marijuana will remain a Schedule 1 substance under the Controlled Substances Act. Substances in Schedule 1 are determined by the Food and Drug Administration to have no medical use. States that allow marijuana for medical use or legalize recreational use remain in defiance of federal law.



The announcement to be published Friday in the Federal Register relaxes the rules for marijuana research to make it easier for institutions to grow marijuana for scientific study. The DEA currently authorizes just one grow facility in Mississippi.



In reaching its conclusion, the DEA said a Health and Human Services evaluation shows marijuana has no ‘‘currently accepted medical use’’ because "the drug’s chemistry is not known and reproducible; there are no adequate safety studies; there are no adequate and well-controlled studies proving efficacy; the drug is not accepted by qualified experts; and the scientific evidence is not widely available."



"There is no evidence that there is a consensus among qualified experts that marijuana is safe and effective for use in treating a specific, recognized disorder," the report added.



"At this time," the DEA concluded, "the known risks of marijuana use have not been shown to be outweighed by specific benefits in well-controlled clinical trials that scientifically evaluate safety and efficacy."



On other points, the DEA report noted marijuana has a "high potential" for abuse and can result in psychological dependence. It said around 19 million individuals in the U.S. used marijuana monthly in 2012 and that contemporaneous studies showed around 4.3 million individuals met diagnostic criteria for marijuana dependence.



It did not find, however, that marijuana is a "gateway drug."



"Little evidence supports the hypothesis that initiation of marijuana use leads to an abuse disorder with other illicit substances," the report said.



The decision signals a difficult road ahead for legalization efforts, said Kevin Sabet, president of Smart Approaches to Marijuana and a former Obama administration drug advisor. Companies that seek to use marijuana as medicine will have to go through the same rigorous scientific evaluation as traditional pharmaceutical drugs.



"This is a vindication for science and for people who have said to go slow," Sabet said. "I think it’s a bad day for legalization efforts and a good day for scientists."



The DEA's decision ignores the public will and patients' experience with the medical benefits of marijuana, says Tom Angell, chairman of Marijuana Majority, which advocates for removing marijuana from the drug scheduling restrictions. Congress should bar DEA and other federal agencies from interfering with the implementation of state marijuana laws, Angell said.



"President Obama always said he would let science — and not ideology — dictate policy, but in this case his administration is upholding a failed drug war approach instead of looking at real, existing evidence that marijuana has medical value," Angell said. "A clear and growing majority of American voters support legalizing marijuana outright and the very least our representatives should do is let states implement their own policies, unencumbered by an outdated ‘Reefer Madness’ mentality that some in law enforcement still choose to cling to."



At least eight states will consider marijuana issues in the November election. Voters in Arizona, California, Massachusetts, Maine and Nevada will consider full legalization. Arkansas and Florida have medical marijuana measures on their ballots. Montana voters will consider a measure to restore the state's medical marijuana law after legislative and judicial actions curtailed the law.