FDA’s top official on Tuesday reported “mounting concerns regarding risks associated with use of kratom," questioning whether use of the botanical could “expand" the nation’s opioid epidemic.

FDA Commissioner Scott Gottlieb, M.D., signaled his agency would step up enforcement activities against distributors of kratom.

“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 in a statement, coinciding with the issuance of a health advisory on kratom. “From the outset, the FDA must use its authority to protect the public from addictive substances like kratom, both as part of our commitment to stemming the opioid epidemic and preventing another from taking hold."

FDA is aware of 36 reports of deaths associated with products containing kratom, Gottlieb said. In addition, reports have surfaced that the botanical has been laced with such opioids as hydrocodone. The use of kratom has also been associated with serious side effects like liver damage, seizure and withdrawal symptoms, he noted.

Gottlieb also reported a 10-fold increase in calls to U.S. poison control centers regarding kratom from 2010 to 2015.

Kratom has been on FDA's radar in recent years, resulting in import alerts and seizures of products. For instance, in September 2014, U.S. Marshals, at FDA’s request, seized raw kratom material worth more than $5 million from Rosefield Management, Inc. in Van Nuys, California.

In 2016, the Drug Enforcement Administration (DEA) announced its intent to temporarily place kratom’s primary active ingredients mitragynine and 7-hydroxymitragynine on the Schedule I list under the Controlled Substances Act (CSA). The agency subsequently withdrew its notice in response to an outcry from Congress and the public.

In response to a request from DEA, FDA conducted a thorough scientific and medical evaluation of two compounds found in kratom, Gottlieb said.

Gottlieb did not specify whether its evaluation has been shared with DEA. A DEA spokesperson did not immediately respond to a request for comment.

Supporters of kratom have rejected claims that the substance has no accepted medical use and a high potential for abuse. However, FDA’s health advisory reinforces the government’s view that kratom is potentially dangerous and has an uncertain future as a legal botanical in the United States.

Susan Ash, founder of the American Kratom Association who stepped down from the organization earlier this year, responded to FDA’s advisory.

“Not only has kratom been used thousands of years around the world safely, I have personally witnessed thousands of people kick their opiate addictions thanks to this plant, without dangerous side effects," she said in an emailed statement. “It seems as though our government wants people to stay addicted during the worst opiate epidemic our nation has ever witnessed, when a simple plant in the coffee family is saving hundreds of thousands of lives from this deadly epidemic."