A sign marking the entrance to the U.S. Drug Enforcement Administration Museum in Arlington, Va. (Jonathan Ernst/Reuters)

A bipartisan group of nine senators is calling on the Drug Enforcement Administration to delay its "unprecedented" decision to ban kratom, a plant that researchers say holds great potential for mitigating the effects of the opioid epidemic.

The DEA recently decided to place kratom into Schedule 1 of the Controlled Substances Act, the most restrictive regulatory category, on a temporary, emergency basis "to avoid an imminent hazard to the public safety."

The Senate letter, spearheaded by Orrin G. Hatch (R-Utah) says: "Congress granted emergency scheduling authority to the DEA based on the need for law enforcement interdiction of new and previously unknown illegal synthetic street drugs that result in injuries and death. The use of this emergency authority for a natural substance is unprecedented, so it is important to determine whether the circumstances here necessitate a jump to Schedule I."

"Given the long reported history of Kratom use," the letter continues, "coupled with the public’s sentiment that it is a safe alternative to prescription opioids, we believe using the regular review process would provide for a much-needed discussion among all stakeholders."

The DEA announced its plan to place kratom in Schedule 1 only one month ago, using an emergency authority that does not require it to solicit public feedback on the decision. Blowback from pain patients was swift and furious and appears to have caught the DEA off-guard.

People who take the plant have shared their stories on how kratom helped them overcome addiction to opiates or alcohol, or how it has helped them treat otherwise intractable pain. Researchers say that their work with the kratom plant could eventually lead to the development of nonaddictive alternatives to powerful opiate painkillers, and that by placing kratom in Schedule 1, the government is effectively crippling their ability to carry out that research.

Over 140,000 people have signed a White House petition asking the Obama administration to reconsider the move.

The DEA cites 600-plus poison-control center calls involving kratom between 2010 and 2015 in its justification for banning the plant, and notes that 15 deaths were linked to the use of the plant between 2014 and 2016. In an interview with The Washington Post, a DEA spokesman later clarified that all but one of those fatalities involved the use of other substances.

Earlier this week 51 U.S. representatives similarly called on the DEA and the White House to reconsider or at least delay the ban, which was slated to go into effect as early as Friday.

In an interview, DEA spokesman Russell Baer confirmed that the ban was not yet in place. "We have not yet determined a date when we will publish that final order" putting the ban into effect, he said.

Because of the uncertainty surrounding the final date of the ban, many online businesses selling the plant have already shuttered or got rid of their supplies for fear of running afoul of the DEA's stringent Schedule 1 rules.

"Given the extremely short timeframe for the implementation of the proposed DEA scheduling order, we urge you to take appropriate steps to delay the order to allow both for a public comment period and sufficient time for the DEA to outline its evidentiary standards to Congress regarding the justification for this proposed action," the letter from Hatch and colleagues concludes.

Baer said the DEA would respond to the senators' and congressmen's concerns, but could not say whether the ban would go into force before that correspondence happens.

"It's not a matter of if. It's simply a matter of when, in terms of DEA publishing the final order to temporarily schedule kratom," Baer said. "Our administrator [Chuck Rosenberg] has determined that kratom represents an imminent hazard to public safety. So I have a sense that publishing our final order will be sooner as opposed to later."

The text of the full letter is available here. The list of Senate signatories, sent by a spokesman for Hatch, is below:

Orrin G. Hatch (R-Utah)

Mike Lee (R-Utah)

Mark Kirk (R-Ill.)

Angus King (I-Maine)

Michael F. Bennet (D-Colo.)

Bernie Sanders (I-Vt.)

Thom Tillis (R-N.C.)

Ron Wyden (D-Ore.)

Mark R. Warner (D-Va.)