Radioligand-binding study of noribogaine, a likely metabolite of ibogaine.

Radioligand-binding studies were performed to ascertain the actions of noribogaine, a suspected metabolite of ibogaine, on opioid receptors. Consistent with previous results, ibogaine showed highest affinity for kappa opioid receptors (Ki = 3.77 +/- 0.81 microM), less affinity for mu receptors (Ki = 11.04 +/- 0.66 microM) and no affinity for delta receptors (Ki > 100 microM). Noribogaine showed a higher affinity than ibogaine for all of the opioid receptors: kappa Ki = 0.96 +/- 0.08 microM, mu Ki = 2.66 +/- 0.62 microM and delta Ki = 24.72 +/- 2.26 microM. These data suggest that noribogaine is active in vivo and that it may contribute to ibogaine's pharmacological effects.