Starting today, the US Drug Enforcement Administration is free to list a popular herbal supplement called kratom as a Schedule I controlled substance. This would put kratom in the same lineup as heroin and make its sale and use a felony. But, in statements to the press, the agency said it has no timetable for officially listing kratom—it could be next week or longer—leaving users on the edge of their seats.

Since the DEA announced its plan to ban kratom at the end of last month, thousands of users have frantically sought to reverse the decision, as well as buy up as much of the drug as they can. Users claim kratom, or Mitragyna speciosa, a tree in the coffee family, is effective at treating chronic pain, as well as depression, anxiety, PTSD, and other ailments. The main active ingredients in kratom are mitragynine and 7-hydroxymitragynine, which can interact with opioid receptors in the brain. While the data to back up medical use of the plant is scant, users are adamant that it's a lifesaver, allowing them to kick deadly and all-too-common opioid addictions.

Since late August, more than 140,000 people have signed a petition asking the Obama administration to keep the DEA from banning kratom. On September 13, hundreds marched in front of the White House, hoisting signs that read “Kratom Saved Me” and sharing personal stories of how the drug got them off of opioid pain killers.

Their efforts got the attention of lawmakers. Last week, 50 members of the House of Representatives signed a letter sent to the DEA urging the agency to delay listing kratom as a Schedule I until it can collect more information from the public and researchers. The letter, spearheaded by Mark Pocan (D-Wis.) and Matt Salmon (R-Ariz.), cites ongoing research into the use of kratom as a treatment for opioid withdrawal. “The DEA’s decision to place Kratom as a Schedule I substance will put a halt on federally funded research and innovation surrounding the treatment of individuals suffering from opioid and other addictions—a significant public health threat,” the letter reads. Any such listing of a potentially useful drug should not be done in haste, lawmakers argue.

Now a similar letter, written by Senator Orrin Hatch (R-Utah) is circulating through the Senate, gathering signatures.

Part of Congress’ objection to the DEA’s ban is the way the agency went about it. Usually, listing a drug involves a lengthy review, with input from the Food and Drug Administration and the public. But in this case, the agency made an emergency, unilateral decision based on the view that kratom presents a “public health crisis.” The emergency action means the DEA can temporarily add kratom to its list of Schedule I drugs. And in two or three years, that temporary listing can become permanent. The agency based its emergency action on the increasing importation of kratom, as well as the drug’s opioid-like effects and addictiveness. According to the DEA, US poison control centers received 660 calls about kratom use between 2010 and 2015.

But lawmakers, users, and some scientists question the DEA’s claim that kratom is a critical threat. They point to anecdotal information that it’s helping people get off of opioids. Critics also note that US poison control centers receive millions of calls, often dealing with laundry detergent and prescription drugs.

Editor's Note: This post was updated to correct the time frame of the 660 poison center calls.