Previous studies on the genus Clusia have shown anti-inflammatory and antiproliferative effects of the leaf extracts,but its antinociceptive activity has never been characterized.In the present study,the antinociceptive activity of the hexane extract of the leaves of Clusia nemorosa G.Mey,called HECn,was examined.Antinociceptive activity was evaluated using acetic acid-induced writhing,formalin,and hot-plate tests.All experiments were carried out on male Swiss mice.The extract(1 400 mg kg 1),given by intraperitoneal route(i.p.) 1 h prior to testing,produced a dose-dependent inhibition on the number of abdominal writhings,with an ID50 of 62 mg kg 1.In addition,HECn was able to prevent the visceral pain induced by acetic acid in mice for at least 2 h.In the formalin test,HECn had no effect in the first phase,but produced an analgesic effect on the second phase with the inhibition of licking time.The HECn did not show a significant analgesic effect in the hot plate test.Pretreatment with yohimbine attenuated the antinociceptive effect induced by HECn in the writhing test.However,naloxone,atropine,or haloperidol did not affect antinociception induced by HECn in the writhing test.Together,these results indicate that the extract from the leaves of Clusia nemorosa produces antinociception in models of chemical pain through mechanisms that suggest participation of the adrenergic systems pathway. Previous studies on the genus Clusia have shown anti-inflammatory and antiproliferative effects of the leaf extracts, but its antinociceptive activity has never been characterized. In the present study, the antinociceptive activity of the hexane extract of the leaves of Clusia nemorosa G. Mey, called HECn, was examined. Antinociceptive activity was evaluated using acetic acid-induced writhing, formalin, and hot-plate tests. All experiments were carried out on male Swiss mice. extract (1 400 mg kg 1), given by intraperitoneal route ip) 1 h prior to testing, produced a dose-dependent inhibition on the number of abdominal writhings, with an ID50 of 62 mg kg 1. In addition, HECn was able to prevent the visceral pain induced by acetic acid in mice for at least 2 h.In the formalin test, HECn had no effect in the first phase, but produced an analgesic effect on the second phase with the inhibition of licking time. The HECn did not show a significant analgesic effect in the hot plate test. Pleat withyohimbine attenuated the antinociceptive effect by HECn in the writhing test. However, naloxone, atropine, or haloperidol did not affect antinociception induced by HECn in the writhing test. Together these results indicate that the extract from the leaves of Clusia nemorosa produces antinociception in models of chemical pain through mechanisms that suggest participation of the adrenergic systems pathway.