The fate of a popular Southeast Asian plant product called kratom is uncertain following a Tuesday warning from the Food and Drug Administration, which says it’s seeking to stop imports of the tree leaf commonly used for pain management and addiction recovery.

Kratom tastes like green tea when it’s brewed and sometimes is taken as a pill. It comes from tropical trees related to coffee and users say it improves moods, gives an energy bump and alleviates pain. Proponents buy it online or at gas stations to treat arthritis, anxiety, and depression.

Many recovering heroin addicts use kratom to wean themselves off cravings, and its proclaimed benefits led the Drug Enforcement Administration to back off plans for an emergency ban last year.

The FDA’s Tuesday statement was not coordinated with the DEA and says the FDA is exercising authority over kratom as an unapproved drug. The DEA did not immediately release a statement on whether it intends to take action of its own.

In the agency’s statement, FDA Commissioner Scott Gottlieb warned that kratom can cause seizures and liver damage, as well as addiction and that its use as a non-traditional medicine is alarming without further research.

“Given all these considerations, we must ask ourselves whether the use of kratom – for recreation, pain or other reasons – could expand the opioid epidemic,” Gottlieb wrote.

He continued: “To fulfill our public health obligations, we have identified kratom products on two import alerts and we are working to actively prevent shipments of kratom from entering the U.S. At international mail facilities, the FDA has detained hundreds of shipments of kratom. We’ve used our authority to conduct seizures and to oversee the voluntary destruction of kratom products.”

To avoid potential problems with the FDA, many kratom vendors already attach labels saying it is not intended for human consumption. It’s unclear if this will be enough to prevent FDA action.

FDA spokeswoman Lyndsay Meyer said, “the FDA looks at a range of information to determine if enforcement is appropriate.”

Because kratom trees cannot grow in most of the continental U.S., a serious effort to ban imports could dry up supplies.

Research suggests two compounds in kratom — mitragynine and 7-hydroxymitragynine -- are partial agonists of the mu opioid receptor, triggering a similar but less intense reaction than other drugs.

“That is the same target that heroin, morphine and fentanyl bind to," Columbia University researcher Andrew Kruegel said last year. "The key thing from the science side is they activate this receptor in a different way. For one, they are partial agonists, which means they stimulate the receptor to a lower level … no matter how high you go with the dose."

The FDA’s announcement is likely to reopen debate and activism following a one-year lull.

Last fall, dozens of members of Congress sided with consumer and industry groups requesting regulatory restraint after a large rally outside the White House, where users distributed tea in Solo cups to passersby and chanted “it’s a plant!” to protest a looming DEA ban.

“Kratom saved me, I was a bad heroin addict,” David Allen of Chapel Hill, N.C., said at last year’s White House rally. “It keeps cravings away and helped me not drink. I came because I don’t want to lose my medicine.”

Brad Miller, a physics teacher at Spotsylvania High School in Virginia, said at the rally he sipped the tea to treat arthritis. He said he went on a weeklong camping trip and – unlike some users – “I didn’t have withdrawal symptoms, but I did have arthritis pain.”

The DEA said in October 2016 it would hold off on banning kratom as a Schedule I substance, pending additional public comment and evaluation and scheduling recommendation from the FDA. It's not yet clear how the DEA will respond to the FDA’s advisory.

In his statement, Gottlieb said “there’s clear data on the increasing harms associated with kratom,” citing calls to poison control centers and that the FDA “is aware of reports of 36 deaths associated with the use of kratom-containing products.”

The claims of associated deaths are likely to be closely scrutinized. Last year, when the DEA cited 15 associated deaths, the American Kratom Association consumer group claimed that it hired a toxicologist to review those reports and found each case could be attributed to other drugs.

Kratom advocates point out that nearly 55,000 people are believed to have died from other opioids in 2016 alone: about 20,000 from fentanyl -- legal for some medical uses -- and its analogs, about 15,000 each from other legal prescription opioids and illegal heroin, and more than 3,000 from methadone, a legal treatment that allows opioid addicts an off-ramp from cravings.

Meyer said additional information on the 36 deaths associated with kratom use requires Freedom of Information Act requests for adverse event reports, with three such requests triggering public release following redactions.

Gottlieb’s statement said ”the FDA has conducted a comprehensive scientific and medical evaluation of two compounds found in kratom,” but the findings were not released.

“The eight-factor analysis will be shared if/when the DEA makes their scheduling decision,” Meyer said.

Many consumer activists, businesspeople, and politicians did not promptly comment on the FDA development Tuesday, as its potential impact was not immediately clear.

Although some people addicted to heroin or prescription opioids say kratom has helped them to transition into recovery, there’s significant anecdotal evidence that kratom can itself lead to dependence.

Paul Pelosi Jr., now the former volunteer executive director of the American Kratom Association, said in an interview last year he believed between 4 million and 5 million Americans were using kratom, based on his understanding of industry sales figures.

Pelosi, the son of House Minority Leader Nancy Pelosi, D-Calif., said the product is “pretty safe.”

“It may be slightly addictive, but there’s no overdose or safety issue,” he said. "It’s not just a couple of teens trying to get high. There’s limited party use for this.”