The effects of Rhynchophylline, Corynoxeine, and Isocorynoxeine, isorhynchophylline-related alkaloids present are tested in Uncaria species, on 5-MeO-DMT-induced head-twitch behaviour in reserpinized mice. Neither Rhynchophylline [H=1.369, P=0.504] nor Corynoxeine [H=0.242, P=0.886] affects the behaviour, while Isocorynoxeine significantly attenuates it at 30 mg/kg (i.p.) [H=7.582, P<0.01].