Introduction: Immune system is involved in the etiology and pathophysiology of inflammation and vitamins are important sources of substances inducing nonspecific immunomodulatory effects. Given the proinflammatory role of cytokines in the inflammation and pain induction, this study aimed to assess the effects of long-term administration of vitamin B1 on the proinflammatory cytokines, edema, and hyperalgesia during the acute and chronic phases of adjuvant-induced arthritis. 
Methods: On the first day of study, inflammation was induced by intraplantar injection of complete Freund’s adjuvant (CFA) in the hindpaws of rats. Vitamin B1 at doses of 100, 150, and 200 mg/kg was administrated intraperitoneally during 21 days of the study. Antinociceptive and anti-inflammatory effects of vitamin B1 were also compared to indomethacin (5 mg/kg). Inflammatory symptoms such as thermal hyperalgesia and paw edema were measured by radiant heat and plethysmometer, respectively. Serum TNF-α and IL-1ß levels were checked by rat standard enzyme-linked immune sorbent assay (ELISA) specific kits. 
Results: The results indicated that vitamin B1(150 and 200 mg/kg) attenuated the paw edema, thermal hyperalgesia, and serum levels of TNF-α and IL-1ß during both phases of CFA-induced inflammation in a dose-dependent manner. Effective dose of vitamin B1(150 mg/kg) reduced inflammatory symptoms and serum levels of TNF-α and IL-1ß compare to indomethacin during the chronic phase of inflammation. 
Conclusion: Anti-inflammatory and antihyperalgesic effects of vitamin B1 during CFA-induced arthritis, more specifically after chronic vitamin B1 administration, suggest its therapeutic property for inflammation.