Purpose: To determine, in Sprague Dawley rats, the toxicity profile of the methanol extract of Mentha spicata, a plant used in folklore medicine for the treatment of various forms of pain.

Methods: The plant extract, at concentrations ranging from 100 - 0.07 mg/ml, was used to determine the median lethal concentration  (LC₅₀) based on brine shrimp lethality assay. Artificial sea water served as control. Acute oral toxicity testing was carried out, according to the Organisation for Economic Co-operation and Development (OECD) guidelines, based on serum biochemical analysis and histological investigations of liver, kidney, heart, spleen and lungs.

Results: The LC₅₀ value of Mentha spicata was 1701 µg/ml in brine shrimp lethality assay, indicating that the plant extract is non-toxic. For acute toxicity testing, administration of a single dose of 5000 mg/kg extract to the rats did not produce toxicity, in terms of changes in behaviour or mortality. Moreover, the weight of major organs of the animals did not significantly (p > 0.05) differ from those of the control group. No toxicologically significant (p > 0.05) hematological and biochemical changes were noticed between animals treated with the plant extract and control animals. Treatment with plant extract did not cause any morphological changes in the heart, liver, kidney and lung tissues of the rats. Histopathological examination also did not reveal any toxicity evidence in the extract-treated animals.

Conclusion: The results obtained suggest that the plant extract can be classified as non-toxic.