Summary
A medRxiv preprint reports that chemical testing found undeclared kratom-related compounds in all 46 products sampled under a cat’s claw label. Five also contained tianeptine, an antidepressant not approved in the United States.
A medRxiv preprint reports that laboratory testing found undeclared kratom-related compounds in all 46 products sampled under a cat’s claw label. Five products also contained tianeptine, an antidepressant not approved in the United States. The findings describe the chemical contents of a specific set of products, not health outcomes in people who used them.
The researchers bought chewable or unit-dose products from online retailers and three gas stations in Mississippi in September 2026. The 46 products represented 17 brands. None declared kratom alkaloids or their derivatives on the label, according to the study.
What testing found
Mitragynine was detected and quantified in 41 products (89%; 95% confidence interval, 76% to 96%). The kratom-related compound 7-hydroxymitragynine (7-OH) was present in 35 (76%; 95% CI, 61% to 87%). Testing also found MGM-15, or dihydro-7-hydroxymitragynine, in 24 (52%; 95% CI, 37% to 67%) and mitragynine pseudoindoxyl (MP) in 22 (48%; 95% CI, 33% to 63%).
In total, 39 products (85%; 95% CI, 71% to 94%) contained MP or MGM-15. The authors report that the US Drug Enforcement Administration temporarily placed both compounds in Schedule I in August 2026. The amount of 7-OH varied substantially, from 0.01 to 95.4 milligrams per unit.
Tianeptine was found in five products (11%; 95% CI, 4% to 24%), at 27.9 to 40.2 mg per unit. The authors also found mitragynine, 7-OH and 3-dehydromitragynine in eight products whose labels included claims such as “NO KRATOM and No 7-OH” or “NO 7-OH.”
How the products were analysed
The team extracted product samples with methanol and compared them with an extract of botanically verified Uncaria tomentosa bark, the plant known as cat’s claw. They used ultra-high-performance liquid chromatography with photodiode array detection, then liquid chromatography–quadrupole time-of-flight mass spectrometry to identify additional compounds. Quantities were calculated against authentic reference standards.
This was a cross-sectional chemical analysis of products, rather than a study of consumers. It establishes what the tested units contained; it does not measure the effects of using them or the frequency of related illness. The authors say labels offered no reliable guide to exposure and recommend that clinicians assessing unexplained opioid toxicity after cat’s claw product use consider kratom-derived opioids and tianeptine.
The sample was drawn from online sellers and a small number of locations in Mississippi. Its percentages therefore describe the products tested, not the share of all products sold under cat’s claw labels.