Materials and Methods: Forty‑two male rats were assigned randomly to two experimental groups and one control group. Nickel–titanium coil springs were used to exert orthodontic force. The rats in the control group and experimental group‑1, respectively, received a daily injection of 0.1 ml of normal saline and 10 mg/kg of tramadol for 14 days. The rats in experimental group‑2 received 10 mg/kg of the same drug on days 1-4, 20 mg/kg on days 5-8, 40 mg/kg on days 9-12 and 60 mg/kg on days 13 and 14. OTM was measured on days 4, 8, 12, and 14. At the end of the experimental period, the rats were sacrificed. Histological analysis was also performed to evaluate the number of osteoclasts, osteoblasts, and Howship’s lacunae. 

  Results: Statistical analysis with analysis of variance tests showed that the rats in experimental group‑2 had significantly decreased OTM compared with the other two groups (P < 0.05), whereas OTM for the rats in experimental group‑1 was comparable to that in the control group (P > 0.05). The histological evaluations did not show any significant difference among the groups (P > 0.05). 

  Conclusion: The effect of tramadol hydrochloride on OTM depends on the dosage used. High doses of the drug reduce the extent of OTM significantly.