Background & Objective: Silymarin is an effective material of Milk thistle whose therapeutic effects have been mentioned in folk medicine. However, little research has been conducted on its antinociceptive effect and its mechanisms of action. Therefore, the aim of present study was to investigate the pain-relieving effects of silymarin using Formalin test with an emphasis on histaminergic system in rats.
Materials & Methods: In this experimental study, 42 male rats weighing approximately 200-250 g aged 12-14 weeks were divided into 7 groups with 6 rats in each group: control group (Saline + Formalin 1% intraplantar), 4 treatment groups with silymarin (50, 100, 200 and 400 mg/kg), 1 treatment group with chlorpheniramine (20 mg/kg), 1 pretreatment group with chlorpheniramine (20 mg/kg) + silymarin (200 mg/kg). Formalin test was used to assess somatic pain. One-way ANOVA was used to analyze the data.
Results: Intraperitoneal injection of silymarin significantly reduced pain response in both the first and second phase of formalin pain (P<0.05). Pretreatment with chlorpheniramine and then silymarin enhanced the analgesic response in both phases of formalin pain (P<0.05).
Conclusion: Silymarin has analgesic effects and these effects are probably caused by using the histaminergic system.