(CNN) The Food and Drug Administration dealt another blow Tuesday to supporters of kratom, warning about "deadly risks" associated with the botanical supplement often used to treat pain, anxiety and depression. Kratom also has opioid-like effects -- at low doses, it acts like a stimulant; at higher doses, it sedates, dulling pain -- which has also made it popular as an over-the-counter remedy for opioid withdrawal.

"It's very troubling to the FDA that patients believe they can use kratom to treat opioid withdrawal symptoms," FDA Commissioner Scott Gottlieb said in a statement . "There is no reliable evidence to support the use of kratom as a treatment for opioid use disorder."

Instead, he said, the FDA is concerned that the use of kratom could actually "expand the opioid epidemic."

"We've learned a tragic lesson from the opioid crisis: that we must pay early attention to the potential for new products to cause addiction and we must take strong, decisive measures to intervene," Gottlieb said.

Gottlieb pointed to reports of 36 deaths associated with kratom, as well as a tenfold increase in calls to US poison control centers about the substance between 2010 and 2015.

Gottlieb said kratom has been associated with "serious side effects like seizures, liver damage and withdrawal symptoms." In addition, he said, kratom can be laced with other pain medications, like hydrocodone, contributing to opioid addiction.

Used for centuries

Native to Southeast Asia, the kratom tree's leaves have been used for centuries as an herbal drug by laborers and farmers. Today, leaves are ground into pills and powders and sold as a dietary supplement. It can be found in head shops and online. It's even made into drinks in some bars

Kratom has a narcotic effect because its active ingredients, the alkaloids mitragynine and 7-hydroxymitragynine, bind to the opioid receptors in our body, according to Dr. Ed Boyer , a professor of emergency medicine at the University of Massachusetts Medical School, who has studied the plant. But unlike opioid drugs such as hydrocodone or heroin, it doesn't appear to slow breathing, he said.

Recent research has shown that one of the two active ingredients, 7-hydroxymitragynine, can be several times more potent than morphine, Boyer said.

But a study to be presented to the Society of Neuroscience shows the other alkaloid, mitragynine, isn't addictive and may indeed have therapeutic effects, said medical chemist Chris McCurdy, a professor at the University of Florida and one of the authors of the new research who has been studying kratom for more than a decade.

"I share the public health concerns," McCurdy said. "I'm not beating a drum to keep it legal and keep it the wild wild West. But I truly believe that it has medical potential."

Scott Hemby , McCurdy's research partner, was skeptical of kratom when they started their work but has since changed his mind. "I think it has the potential to be a pharmacotherapy, but we need to do more studies. "

Hemby, who studies the abuse potential of drugs at High Point University, said he hasn't seen any data to prove that both active ingredients are as addictive as the FDA has stated.

"I'm concerned that we may be pushing the boat out of the harbor before we really know what's going on," he said. "The scientific community needs more time to definitively state one thing or another. I would hope public policy would be driven by scientific evidence."

Regulatory ups and downs

Kratom has come under fire before. In 2014, the FDA issued an alert that allowed US officials to detain kratom without a physical examination. Between February 2014 and July 2016, the DEA said , nearly 247,000 pounds of kratom were seized.

In August 2016, the Drug Enforcement Agency moved to make kratom a Schedule I drug , a substance that has "no currently accepted medical use and a high potential for abuse." After a public outcry, including letters from members of the House of Representatives and the Senate on the possible benefits of kratom, the DEA withdrew its intent to make it Schedule I. Instead, it opened a public comment period to react to possible scheduling, which closed in December 2016. Since that time, the DEA has taken no action and says they are still in the review process.

A call to science

In his statement, Gottlieb addressed the concerns of those interested in more science, saying that although the FDA remains open to the potential medicinal uses of kratom, "those uses must be backed by sound-science and weighed appropriately against the potential for abuse" and thoroughly evaluated by the DEA and the FDA.

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"To those who believe in the proposed medicinal uses of kratom," he wrote, "I encourage you to conduct the research that will help us better understand kratom's risk and benefit profile, so that well studied and potentially beneficial products can be considered."

At the request of the DEA, Gottlieb said, his agency has conducted a comprehensive scientific and medical evaluation of two compounds found in kratom and continues to actively prevent shipments from entering the country, and to destroy any that are seized.

"If they've been doing a review of the work for a year, who's been doing the science? And why hasn't anyone contacted us?" asked McCurdy, who has studied the plant for 13 years. Even though his name is frequently found as an author on kratom studies, he said, he was not approached by the FDA for its review.

"I realize there hasn't been a huge amount of science, but that's where we are now at: getting some of this science to the forefront," McCurdy said. "Obviously, I agree with the need to regulate the marketplace, but I don't want it to impede the research and potential for a treatment."