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

Abstract 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 κ opioid receptors ( K i = 3.77 ± 0.81 μ M), less affinity for μ receptors ( K i = 11.04 ± 0.66 μ M) and no affinity for δ receptors ( K i > 100 μ M). Noribogaine showed a higher affinity than ibogaine for all of the opioid receptors: κ K i = 0.96 ± 0.08 μ M, μ K i = 2.66 ± 0.62 μ M and δ K i = 24.72 ± 2.26 μ M. These data suggest that noribogaine is active in vivo and that it may contribute to ibogaine's pharmacological effects.