The U.S. government's classification of cannabis as a Schedule I drug is impeding medical marijuana research, a leading think tank said Tuesday, in what it called a misstep that could impact advancements in health care.

“As medical marijuana becomes increasingly accessible in state-regulated, legal markets, and as others self-medicate in jurisdictions that do not allow the medical use of cannabis, it is increasingly important that the scientific community conduct research on this substance,” said the report by Brookings Institution public policy analysts John Hudak and Grace Wallack.

“However, statutory, regulatory, bureaucratic, and cultural barriers have paralyzed science and threatened the integrity of research freedom in this area.”

Medical marijuana is currently legal in 23 states and Washington, D.C. Researchers have said marijuana can, for example, help reduce appetite loss associated with cancer and AIDS and relieve anxiety and insomnia.

The Drug Enforcement Administration (DEA) has repeatedly rejected calls to change marijuana’s classification as a Schedule I drug, defined as a substance without accepted medical use that is likely to be abused. The report suggested that Congress amend the Controlled Substances Act to designate cannabis as a Schedule II drug — one with accepted medical use but high potential for abuse — “or to another schedule or off the lists altogether.”

The report argued that marijuana’s designation as a Schedule I drug may prevent medical institutions and professions from “staking their own reputations” on marijuana research.

“Moving marijuana from Schedule I to Schedule II would signal to the medical community that FDA and NIH are ready to take medical marijuana research seriously, and help overcome a government-sponsored chilling effect on research that manifests in direct and indirect ways,” the report said, referring to the Food and Drug Administration and the National Institutes of Health.

Reclassifying marijuana as a Schedule II drug would still only slightly shift perceptions on research, the report said, because Schedule II drugs are defined as viable for medical purposes but as having a high potential to be abused.

Beyond shifting the culture surrounding medical marijuana research, changing marijuana’s designation would mean less legal restrictions on research.

“DEA, FDA, and state law all require levels of licensing and registration for conducting research with Schedule I drugs. Researchers hoping to obtain approval for research with marijuana (or any Schedule I drug for that matter) go through a multi-agency registration and review process,” the study said.

Restrictions imposed by the government have also included what the report calls a “monopoly” on research marijuana. The DEA has mandated that all research must use marijuana grown at a University of Mississippi facility commissioned by the National Institute on Drug Abuse (NIDA).

"Removing the DEA-mandated NIDA monopoly ... would all go a long way to improve the scientific community’s capacity and ability to study marijuana for medical use," the report said. "It's time to stop letting outdated policy prevent the scientific community from advancing knowledge and ensuring that patients and practitioners understand the benefits and risks of medical marijuana."