The U.S. Food and Drug Administration is escalating its campaign against kratom with the release of new information describing a series of deaths involving the popular herbal drug.

The FDA says the incidents underscore the serious and sometimes deadly risks of kratom, but the list contains a number of events in which kratom played an uncertain role, including a case in which a teenager hanged himself, and another in which a drug overdose victim tested positive for nine different substances.

As a whole, the data suggests the FDA is basing its warnings about kratoms fatal harms on a patchwork of loosely sourced anecdotal reports that say very little about how the drug is responsible for the fatalities or even whether it is at all.

In a press release Tuesday, FDA Commissioner Scott Gottlieb sought to reinforce a November public health advisory in which he claimed there was clear data on the increasing harms associated with kratom. At the time, the FDA said it was aware of 36 deaths involving kratom, which it held up as evidence of the gravest of the drugs potential harms. The FDA has found eight additional cases since then, Gottlieb said Tuesday, bringing the total number of kratom-associated deaths to 44. He also announced the agency had conducted a novel scientific analysis of kratom that further supports the FDAs characterization of the substance as an opioid.

This new data adds to our body of substantial scientific evidence supporting our concerns about the safety and abuse potential of kratom, said Gottlieb. As the scientific data and adverse event reports have clearly revealed, compounds in kratom make it so it isnt just a plant its an opioid.

Kratom is an herb derived from the leaves of a Southeast Asian tree related to coffee. Its sold in the U.S. as an unregulated herbal supplement and commonly taken in powder form in capsules or tea. Kratom has opioid-like effects and is often used as a mood enhancer, or for its stimulant or sedative qualities, which can vary depending on the dose and strain. Supporters regularly tout it as a natural treatment for conditions like chronic pain, anxiety and depression. Others claim its a safer alternative to traditional opioids, both legal and illegal, which has also contributed to kratoms increasing popularity as a step-down treatment off of painkillers or heroin.

But due to the lack of regulations around herbal supplements, kratom is largely free from consumer standards on quality or dosing, leading to fears about the possible adulteration of products and problems related to improper self-medication or misuse by youth. The FDA has maintained that kratom is dangerous, and has pointed to the lack of an approved medical use as justification to impound numerous shipments of kratom products into the U.S.