The compound PT-31, 3-(2-cloro-6-fluorobenzil)-imidazolidine-2,4-dione, is a promising derivative of imidazolidine with proven agonist activity at the α2A-adrenergic receptors, that displays analgesic dose-dependent and synergistic action profile with morphine. This study evaluates the toxicity, cytotoxicity and mutagenicity of PT-31 on Allium cepa L. Three graded dosages with dilution ranging from 0.5 to 5.0 mg/mL were used in the present study, with dechlorinated water and copper sulphate (0.0006 mg/mL) as negative and positive controls, respectively. After 72 hours of exposure, the roots were measured and removed. Analyses of root growth and mitotic index were used to assess the toxicity and cytotoxicity. Mutagenicity was identified by the frequencies of chromosomal aberrations and of micronuclei. The PT-31 inhibited the mitotic index and root growth at a dose of 5.0 mg/mL (P < 0.001) and increased frequencies of chromosomal aberrations and micronuclei at a dose of 1.0 mg/mL (P < 0.05). These data indicate toxicity, cytotoxicity and mutagenicity of PT-31. Given the clinical potential of PT-31, we suggest additional studies to elucidate the mechanisms that generate the effects observed. The A. cepa test, as well as the Ames test, may be used for pre-clinical tests related to toxicity, cytotoxicity and mutagenicity, and may predict an initial profile of safety and efficacy of the new molecule.