"These reports underscore the serious and sometimes deadly risks of using kratom and the potential interactions associated with this drug", the FDA said.
However, as an unregulated and unapproved psychoactive substance being used without supervision, kratom poses unknown risks.
All of those compounds, they discovered, shared structural similarities with opioids like derivatives of morphine.
But the FDA's concerns over kratom use have grown, with the agency pointing to 44 deaths associated with the plant. They also found that 22 of the 25 compounds in kratom bind strongly to mu-opioid receptors, comparable to opioid drugs.
Gottlieb said that kratom was used to treat pain, anxiety, and depression-and was also being taken recreationally because its effects somewhat mimicked that of more powerful processed opiates. "Further, as the scientific data and adverse event reports clearly revealed, compounds in kratom make it so it isn't just a plant-it's an opioid", Dr. Gottlieb said in the statement. But Hunter noted that some synthetic opioids, like fentanyl and methadone, don't look much like morphine in their structure either.
Hunter added that some synthetic opioids are derived from materials found in coal tar. "Kratom should not be used to treat medical conditions, nor should it be used as an alternative to prescription opioids.".
Opioid Alternative Kratom Is Actually an Opioid Itself, FDA Warns
Although a number of deaths have been linked to use of kratom, it's unclear if the deaths are a direct result of using the drug, Marc Swogger, an associate professor of psychiatry at the University of Rochester Medical Center in NY, told Live Science in a 2016 interview.
Many people killed by kratom often mixed the drug with other substances, including inhaler chemicals and over-the-counter cold and flu medicine.
After the FDA's November announcement, Jack Henningfield, an addiction specialist who works at the drug policy consulting group Pinney Associates, said that surveys of kratom users suggest that many are taking the supplement to help stop using opioids.
But Gottlieb warned that claiming it's harmless because it's "just a plant" is shortsighted and risky. It's sold online and in shops as powders and pills, among other formulations, and has been loosely regulated by the FDA. For example, in 2010, a product called Krypton, which contained both mitragynine and the opioid O-desmethyltramadol, was linked with nine deaths in Sweden, according to the Journal of Medical Toxicology paper. The agency instead called on the FDA to issue a public comment and scientific review of the plant.
The DEA warned in 2016 that kratom has a high potential for abuse and has no now accepted medical use in treatment in the United States and announced plans to place the active chemicals of the plant - Mitragynine and 7-hydroxymitragynine - on the agency's Schedule I of the Controlled Substances Act in December 2016.
Four-star WR Jacob Copeland commits to Florida, mom gets up and leaves
Yet, when Copeland picked up the Florida hat to make his decision, she got up and walked out of frame in disappointment. Copeland said he couldn't "go with his mom" and had to "go with his heart".