Antinociceptive effect of some Argentine medicinal species of Eupatorium.

Eupatorium laevigatum, E. arnottianum and E. subhastatum, plants used in Argentine folk medicine for the treatment of inflammation and pain related problems, were evaluated for analgesic activity. The infusions of these species (500 mg/kg, p.o.) produced a reduction in the number of stretches of 46.6%, 41.5% and 35.6% respectively, in the acetic acid induced writhing test. This antinociceptive effect of the infusions was not reversed by pretreatment with naloxone. The infusions studied did not produce antinociceptive effects when assayed in the hot plate test. These results suggest that the analgesic activity is exerted by a mechanism unrelated to interaction with opioid systems.