Introduction: Since time memorial, herbal medicine has played an important role for relief of various symptoms including pain relief. Many researches have focused on the curative as well as antinociceptive effects of herbal extracts. Cinnamon Zeylanicum has long been prescribed in traditional medicine for the treatment of inflammatory-related diseases such as rheumatisms, bronchitis and muscle pains. However, there is little if any scientific research indicating this effect Methods: This experimental study was carried out in Shaheed Sadoughi Medical School on 25 Wistar Rats (200-300grams) randomly divided into 5 groups. In this study, the analgesic effect of intraperitoneal administration of hydro-alcoholic Cinnamon extract in different doses (50,100,500mg/kg) was assessed by using Formalin Test (for chronic pain) during 1hr. post Formalin injection. Results: Our results indicated that cinnamon extract in high dose (500mg/kg) decreased the chronic pain intensity in the 2nd phase of formalin test. This analgesic effect was significant (P<0.001) as compared with sham group, but the lower doses (50 &100mg/kg) of cinnamon extract did not show any analgesic effect on chronic pain in Formalin Test. Conclusion: Data from this study confirms the analgesic effect of high doses (500mg/kg) of cinnamon extract on chronic pain in Formalin Test which may be due to anti-inflammatory effect of this plant material.

Keywords: Cinnamon, Chronic pain, Rat, Formalin Test

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