The herbal drug kratom is making headlines again with an alarming public health warning. On Thursday, the US Centers for Disease Control and Prevention announced that kratom’s active ingredients were detected in 152 people who died from drug overdoses over an 18-month period. CDC scientists reported that kratom was a cause of death in 91 of these overdose death cases. Almost all of these deaths, however, involved other drugs that are capable of causing fatal overdoses on their own, including fentanyl, heroin, and prescription opioids.

Sold online and in stores as an herbal supplement, kratom has come under fire in the last few years from public health and drug enforcement officials for its opioid qualities. In this most recent study, just seven of the reported deaths involved kratom alone, but even in those cases, experts aren’t totally convinced that the CDC proves kratom is deadly in typical doses. Typical doses of kratom leaf are usually in the range of a few grams, and deaths involving kratom all by itself are so rare as to be extremely controversial. The CDC did not provide information on the doses consumed by the individuals examined in this report.

The report, published in the CDC’s Morbidity and Mortality Weekly Report, draws its results from the State Unintentional Drug Overdose Reporting System, which contains information from local coroners and medical examiners who reported on each suspected overdose death. Using data collected from 27 states between July 2016 and December 2017, CDC researchers concluded that out of 27,338 people who died from overdoses in that time period, 0.56 percent of them tested positive for one of the active chemicals in kratom — mitragynine.

Joseph Palamar, Ph.D., M.P.H., an associate professor of population health at New York University who studies drug use, tells Inverse that in the majority of these kratom-related death cases, the CDC’s report doesn’t offer much clarity on what role the plant-based drug actually played.

“The majority of deaths said to involve kratom as a cause of death involved opioid or opiate use and/or other drugs,” he says. “I’m not a toxicologist, but I wonder to what extent kratom was listed as a cause simply because it was detected — especially in light of co-detection of fentanyl and/or heroin.”

So what sets apart the 152 kratom-involved deaths (which involved additional drugs) from the 91 kratom-caused deaths (which also involved additional drugs)? According to the CDC, that determination was left to the local medical examiners and coroners.

In response to Inverse’s request for clarification, a CDC spokesperson offered the following explanation:

The data showed 152 deaths in which kratom was detected by post-mortem toxicology testing. Of these 152, in 91 of the deaths the medical examiner or coroner who investigated the death determined that kratom/mitragynine was a cause of death and listed it as such on the death certificate. For the remaining 61 deaths, kratom/mitragynine was detected on the post-mortem toxicology testing but was not indicated as a cause of death by the medical examiner or coroner.

And while medical examiners are highly trained professionals who are accustomed to examining a full range of evidence to make their determinations, the fact remains that determining whether someone died from kratom is a much different determination than it is for other, more familiar drugs like heroin or fentanyl. Kratom is so under-studied by the medical community that there is no established dose that doctors agree is deadly. Therefore, the best evidence these medical examiners have at their disposal may often be past reports from other medical examiners, who were working with similarly incomplete information.

Kratom is usually sold either either as loose leaves or powdered leaves in capsules. Wikimedia / Psychonaught

Marc Swogger, Ph.D., an associate professor of psychiatry at the University of Rochester Medical Center who has studied the individual and societal effects of kratom use, tells Inverse that he doesn’t trust the CDC’s report without seeing the full data.

“I have not seen all of the toxicology reports, so I cannot comment directly on cause of death for these individuals,” says Swogger. “What I can say is that I think the CDC’s numbers are highly questionable. Kratom is a plant for which a mechanism for fatalities is unknown; it does not cause significant respiratory suppression, the most frequent cause of death by classical opioid overdose.”

Unfortunately, even though toxicology screens for these overdose deaths clearly exist, a CDC spokesperson tells Inverse that even the CDC does not have access to the original reports.

“Instead, staff in our funded jurisdictions abstract information from the medical examiner and coroner reports into the State Unintentional Drug Overdose Reporting System (SUDORS),” they say.

Without knowing the levels of mitragynine detected in each person’s body, it’s impossible to know how medical examiners made their determinations in each of the cases. It’s even possible that, since kratom is such an unfamiliar substance to medical examiners, the mere presence of the chemical is enough for them to rule that it caused a death. But without the case reports, there’s no way to know.

Swogger also notes that federal regulators don’t exactly have a sterling history when it comes to reporting on deaths related to kratom. In February 2018, the US Food and Drug Administration issued a series of case reports that officials said showed evidence of 44 deaths involving kratom since 2009. As Inverse reported, those cases had the same issue as those in the most recent CDC report: Almost all of them also involved additional drugs, any one of which could be fatal on its own in sufficient quantities.

“The problem is that many so-called ‘kratom deaths’ have occurred in people who were on other drugs or medications or had other conditions that could have been responsible,” Swogger says. “There is no scientific backing for the idea that kratom is deadly for a significant number of users. Rather, the science to date indicates that it may be doing more good than harm by enabling people — many of whom would not present at a medical center — to self-treat opioid addiction or pain with some success.”

Editor’s Note: As of 11:33 A.M. Eastern, 4/16/19, this story has been updated to include the CDC’s response to our request for the original medical examiner reports.