A new analysis by scientists at the US Food and Drug Administration (FDA) shows that compounds in kratom act like prescription-strength opioids, the agency said today.

The agency also said kratom has now been linked to 44 deaths, up from 36 reported in November.

The scientific data and adverse event reports have "clearly revealed" that compounds in kratom make it "not just a plant — it's an opioid," FDA Commissioner Scott Gottlieb, MD, said in a statement.

"And it's an opioid that's associated with novel risks because of the variability in how it's being formulated, sold, and used recreationally and by those who are seeking to self-medicate for pain or who use kratom to treat opioid withdrawal symptoms," added Dr Gottlieb.

"Claiming that kratom is benign because it's 'just a plant' is shortsighted and dangerous," he added.

FDA scientists analyzed the chemical structures of the 25 most common compounds in kratom and concluded that all of the compounds share structural characteristics with controlled opioid analgesics, such as morphine derivatives. They also found that compounds in kratom bind strongly to mu-opioid receptors, comparable to opioid drugs.

"Based on the data we now have, we feel confident in calling these compounds opioids," Dr Gottlieb said.

Annual Death Rate

To date, the FDA has received 44 reports of deaths associated with the use of kratom. This is an increase since the agency's November 2017 advisory, which noted 36 deaths associated with kratom, as reported by Medscape Medical News.

"We're continuing to review the newly received reports and will release those soon. But it's important to note that these new reports include information consistent with the previous reports," Dr Gottlieb said.

The FDA said that although many of the reports they've received could not be fully assessed, owing to limited information, they are especially concerned about one new report concerning an individual who had no known history or toxicologic evidence of opioid use except for kratom. "We're continuing to investigate this report, but the information we have so far reinforces our concerns about the use of kratom," Dr Gottlieb said.

The FDA is also concerned about a number of kratom-associated deaths in which kratom was combined with other drugs that affect the brain, including illicit drugs, prescription opioids, benzodiazepines, and over-the-counter medications, such as the antidiarrheal medicine loperamide (Imodium, Johnson & Johnson).

"Cases of mixing kratom, other opioids, and other types of medication are extremely troubling because the activity of kratom at opioid receptors indicates there may be similar risks of combining kratom with certain drugs, just as there are with FDA-approved opioids," Dr Gottlieb said.

"Taken in total, the scientific evidence we've evaluated about kratom provides a clear picture of the biologic effect of this substance. Kratom should not be used to treat medical conditions, nor should it be used as an alternative to prescription opioids. There is no evidence to indicate that kratom is safe or effective for any medical use," Dr Gottlieb said.