WASHINGTON (Reuters) - The U.S. Justice Department on Thursday unveiled a historic proposal to ease restrictions on marijuana, a rule that if enacted would also enable more research on its medicinal benefits.

The proposal, first announced in April, would reclassify cannabis from a so-called schedule one drug to a schedule three. Schedule one drugs, such as heroin, are considered highly addictive with no medical benefits, while schedule three drugs are considered to have a moderate to low potential for physical and psychological dependence.

The U.S. Food and Drug Administration said it found "some credible scientific support for the use of marijuana in the treatment of chronic pain, anorexia related to a medical condition, and nausea and vomiting."

"Additionally, no safety concerns were identified in the FDA's review that would indicate that medical use of marijuana poses unacceptably high safety risks," the proposal says.

President Joe Biden, a Democrat who is running for reelection in November, initiated a review of the drug's classification in 2022, fulfilling a campaign promise that was important to left-leaning members of his political base.

Currently, the drug falls under the Drug Enforcement Administration's (DEA) class that includes heroin and LSD. It would be moved to a group that contains ketamine and Tylenol with codeine.

Reclassifying marijuana represents a first step toward narrowing the chasm between state and federal cannabis laws. The drug is legal in some form in nearly 40 states.

While rescheduling the drug does not make it legal, it would open up the doors to more research and medical use, help lead to potentially lighter criminal penalties and increase investment in the cannabis sector.

In a new legal opinion made public on Thursday, the Justice Department's Office of Legal Counsel criticized the DEA's long-held approach for how it determines whether a drug has an acceptable medical use, calling it "impermissibly narrow."

The opinion also found that the DEA should "accord significant deference" to the U.S. Department of Health and Human Services' (HHS) scientific and medical determinations.

According to the proposal, HHS's assistant secretary for health recommended that the DEA should place marijuana into schedule three back in August 2023.

The DEA, however, has yet to make its own determination.

If marijuana's classification were to ease at the federal level, cannabis companies could reap significant benefits, such as being eligible for listing on major stock exchanges and more generous tax deductions.

Moreover, they could face fewer restrictions from banks. With marijuana illegal federally, most U.S. banks do not lend to or serve cannabis companies, prompting many to rely on cash transactions.

The public will get 60 days to submit comments on the Justice Department's proposal.

A public hearing on the proposal can also be requested.

(Reporting by Sarah N. Lynch; Editing by Bill Berkrot)

By Sarah N. Lynch