Introduction: Many neurotransmitters in the central nervous system are involved in pain perception and modulation. Isoniazid, as an important anti-tuberculosis drug, is also a modulator of the GABAergic system in the CNS. As a result, the purpose of the present research was to evaluate the effects of isoniazid on the acetic acid writhing test (a non-selective animal model of pain) in mice. Methods: Four groups of mice (n=8) were used in this study. In this study, the pain was induced by intraperitoneal injection of acetic acid (0.6%, 10 ml/kg) in mice. Saline or isoniazid at doses 25, 50, and 75 mg/kg was administered intraperitoneally 60 min before acetic acid administration. Then, the abdominal writhes were counted during a 30-min period of the test. Results: Isoniazid in doses 25, 50, and 75 mg/kg decreased the number of writhes in the experimental groups compared with the saline-treated group. The dose of 75 mg/kg was the most effective dose of isoniazid in pain reduction. Conclusion: In conclusion, isoniazid has an antinociceptive effect in the writhing test in mice.
