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Background & objectives: Syzygium aromaticum (Clove) is a medicinal plant usually used in traditional medicine to reduce toothache. The aim of the present study was to evaluate the analgesic effect of topical Clove oil on acute and chronic pain in male mice using formalin test.
Methods: In this study, 24 mice were divided into 4 groups: control, morphine (as positive control), Clove oil, and Clove oil plus morphine groups. Before the formalin test, the animals were treated topically with clove oil for 6 hours.  A single dose of morphine (10 mg/kg) was prescribed subcutaneously. Pain scores were obtained using the formalin test through an injection of 20 microliter of formalin 2.5% into the palm of the animal's right hand.
Results: Topical administration of Clove oil significantly decreased acute pain (the initial phase of the formalin test) and chronic pain (the second phase of the formalin test). Furthermore, topical Clove oil increased the analgesic effect of morphine in acute pain phase.
Conclusions: This study showed that the analgesic effect of topical Clove oil was comparable to morphine.