Background and Aim : Isoniazid is an antibiotic that has been used for the treatment of tuberculosis since 1952. However, this drug has also shown some euphoric effects on TB patients. Isoniazid is among the first drugs that suggested having antidepressant effects. However, to our knowledge, there is no report about the antidepressant-like effects of isoniazid in forced swimming test in the laboratory animals. Therefore, this research aimed to evaluate the possible antidepressant-like effects of isoniazid in the forced swimming test. Methods : : In this research, a forced swimming test was conducted to evaluate the possible antidepressant-like effects of isoniazid. Saline and low doses of isoniazid (12.5, 25, 50, and 75 mg/kg, i.p.) were administered to 5 groups of male mice, and the immobility time of the animals was recorded. Moreover, the effects of the low doses of isoniazid on the locomotor activity of the animals were assessed with an open field method. Results : : The mice that received isoniazid 1h before the test showed a significant decrease in the immobility time compared to the saline-treated animals. However, the open field test showed an increase in the locomotor activity in the animals that received isoniazid. Conclusion : The antidepressant-like effects of isoniazid on the reduction in the immobility time in the forced swimming test may be due to its effects on increasing the locomotor activity of the animals.
