Acute oral toxicity and systemic pathological effects of methiopropamine in female ICR mice.

Methiopropamine (MPA) is a stimulant-type new psychoactive substance (NPS) first detected in 2011 and continues to appear in forensic casework across more than 33 countries. Despite its persistence, current knowledge of MPA is largely derived from pharmacological studies, lacking controlled animal study defining its acute oral lethality and associated organ-level toxicity. This study investigated the acute oral median lethal dose (LD50) of MPA in mice using an OECD-compliant approach and acute behavioral effects assessed via the Irwin observational test. Systemic toxicity was further evaluated through gross necropsy and histopathological examination of major organs. The acute oral LD50 of MPA was estimated to be 310 mg/kg, placing it within the moderate toxicity range according to the Hodge and Sterner toxicity scale. Acute exposure produced rapid-onset behavioral toxicity, primarily affecting excitation, motor coordination and stereotypic activity. At a non-lethal dose (175 mg/kg), behavioral effects were transient and resolved within 2 h. In contrast, a lethal dose (550 mg/kg) caused severe, non-reversible neurobehavioral toxicity and death within 1-2 h, accompanied by pericardial blood clots and marked myocardial, hepatic and renal injury. Collectively, these findings define a dose-dependent toxicity profile for oral MPA exposure and provide foundational data to support hazard classification, risk assessment and guide clinical and forensic interpretations in suspected MPA intoxication.