Tanacetum parthenium (T.p.) is used in folk medicine as a treatment wiedly. We reported the analgesic effect of T.p. flowers and leaves previously. This study was designed to find how this mechanism is occurred by T.p. flower extract. Based on our previous study, the dose of 50 mg/kg i.p. of the aqueous extract has analgesic effect on mice (NMRI) (20 ± 2 g) that was used for study. We studied involvement of the opioidergic, serotoninergic,α-adrenergic systems separatly in antinociceptive effect. 15 min before the administration of the extract, animals were pretreated with drugs, including naloxane (5mg/kg, i.p.), serotoninergic antagonist cyproheptadine (4 mg/kg, i.p.) and α-adrenergic antagonist phentolamine (20mg/kg, i.p.)(n > 6 in each group). Pretreatment with naloxane increased pain percepation in the neurogenic phase of formalin test compared to the control (p<0.001). Moreover cyproheptadine increased the sensation of pain in both phases (p<0.05). Inhibition of α -adrenergic system was not be able to attenuate the anti-nociceptive effect of the extract. These results propose the involvement of sertoninergic and opioidergic systems in the anti-nociceptive effect of the T.p. extract.

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