A study in 2019 identified a lethal kratom dosage in mice, or at least a lethal dose of the extracted alkaloids (injected intravenously (i.v.)). For mitragynine, the LD50 (or median lethal dose, the dose that kills 50% of the test population) is apparently 27.8 mg/kg body weight i.v. And for 7-hydroxymitragynine, it’s 24.7 mg/kg body weight i.v. This places the lethal kratom dosage (in mice) roughly in the same region as heroin’s: 27.3 mg/kg body weight i.v.

However, it’s crucial to note the uncommon route of administration; few if any inject. When administered orally, the LD50 for mitragynine in mice was 547.7 mg/kg body weight. No lethal dose was observed for 7-hydroxymitragynine given orally.

So can you overdose on kratom? Probably not—at least not by accident. These findings appear to uphold the broad consensus among users that a lethal kratom dosage (using powdered leaf products as opposed to resins or extracts of unknown potency) would be physically impossible to reach. Doses in excess of 8-9 grams (upwards of 90 mg/kg body weight, say) will induce vomiting far sooner.

Pantano, F. et al. (2016). Hepatotoxicity Induced by “the 3Ks”: Kava, Kratom and Khat. International Journal of Molecular Sciences, 17(4):580