Main targets of ibogaine and noribogaine associated with its putative anti-addictive effects: A mechanistic overview

Ibogaine (IBO), the principal alkaloid of Tabernanthe iboga, has attracted attention as a potential treatment for substance use disorders (SUDs) because preclinical studies report reductions in drug self-administration and relapse for substances including cocaine, ethanol, nicotine and opioids. Human data are limited: case reports and observational series suggest therapeutic effects that can outlast IBO and noribogaine (NOR) pharmacokinetics, and a single randomised, placebo-controlled trial of a T. iboga extract reported prolonged psychoactive effects and reduced cocaine cravings, but cardiac monitoring was not reported. Safety concerns—most notably QT interval prolongation linked to inhibition of hERG channels and rare fatalities—have impeded clinical development, prompting efforts to develop non-hallucinogenic, less cardiotoxic analogues (for example, tabernanthalog). Pharmacokinetic differences between IBO and its main active metabolite NOR (NOR has a substantially longer half-life) have led to suggestions that NOR contributes importantly to prolonged therapeutic and adverse effects. Ona and colleagues set out to update and synthesise the pharmacological targets of IBO and NOR and to discuss how these multi-target actions could underlie putative anti-addictive effects. Rather than seeking a single ‘‘key target’’, the paper frames IBO/NOR activity within a polypharmacology perspective, aiming to map principal receptor and transporter interactions and to consider how combined actions across systems might produce synergistic benefits relevant to different classes of addictive drugs.

The extracted text describes this paper as a literature overview based on a comprehensive search of MEDLINE and Google Scholar up to July 2022, supplemented by articles identified from references of initial papers. Inclusion criteria encompassed both theoretical and experimental studies addressing the pharmacology of IBO and NOR. The document does not present a separate, detailed Methods section typical of systematic reviews (for example, it does not describe a formal study selection flow, risk-of-bias assessment, or prespecified data extraction protocol). Accordingly, the paper synthesises mechanistic evidence from preclinical pharmacology, radioligand binding assays, cellular signalling studies, in vivo animal models, some human pharmacokinetic data, and select clinical and observational reports. When available, quantitative affinity measures (for example Ki values) and functional assay results are reported and discussed alongside behavioural and safety findings to integrate molecular action with potential effects on addictive behaviours.

The review organises findings by principal molecular targets and summarizes key mechanistic data linking IBO/NOR to processes relevant to SUDs. Opioid receptors: Early binding studies suggested MOR interaction, but functional work reported by Alper and others indicates that IBO and NOR act as weak mu opioid receptor (MOR) antagonists (Ki ≈ 3 µM for IBO; 13 µM for NOR) rather than as agonists. Both compounds interact with kappa opioid receptors (KOR); NOR is described as a partial, G-protein-biased KOR agonist. The KOR activity could relate both to IBO’s psychoactive profile and to modulation of reward/anti‑reward systems implicated in addiction. Dopamine transporter (DAT) and dopamine signalling: Early studies reported region- and dose-dependent, biphasic effects of IBO on dopamine (DA). IBO has been reported to inhibit DAT-mediated uptake, though more recent work indicates low DAT affinity and weak direct inhibition. IBO also reduces extracellular DA and increases DA metabolites, consistent with disruption of synaptic vesicle storage via VMAT2 inhibition. In vitro and Drosophila models further suggest IBO/NOR and analogues can interact with DAT to correct folding defects in mutant transporters. The net effect on DA neurotransmission is uncertain because DAT interactions, VMAT2 inhibition and KOR activation (which acutely reduces DA release in nucleus accumbens and dorsal striatum) may oppose one another; preclinical data often show decreases in drug-induced DA efflux after chronic drug exposure. Serotonin transporter (SERT) and serotonin receptors: IBO inhibits SERT and NOR is approximately 10 times more potent as a SERT inhibitor; NOR and IBO increase extracellular 5-HT in vivo. IBO has been characterised as an active-site-binding, non-competitive SERT inhibitor, an unusual enzymological behaviour. Affinity at serotonergic receptors (including 5-HT2A) is weak compared with classical psychedelics; IBO does not elicit the rodent head-twitch response. Nonetheless, SERT inhibition may contribute to antidepressant-like effects and to ameliorating low 5-HT associated with opioid withdrawal. NMDA receptors: IBO acts as a competitive NMDA receptor antagonist in vitro and in vivo; NOR shows lower affinity. NMDA antagonism has complex, region-dependent effects on reward and opioid withdrawal syndrome (OWS): systemic NMDA antagonists can increase or decrease opioid self-administration in different paradigms, whereas local antagonism in VTA or nucleus accumbens can attenuate OWS. The NMDA effects may also relate to antidepressant-like properties similar to ketamine, as suggested by overlapping cortical activity patterns in animal studies. Nicotinic acetylcholine receptors (nAChRs): IBO is a non-competitive antagonist at nAChRs, with particular attention to the α3β4 subtype; it maintains channels in a desensitised state more persistently than some comparators. Given evidence that α3β4 receptors are implicated in opioid withdrawal and that genetic variation in CHRNA3 cluster genes associates with opioid dependence/withdrawal in humans, nAChR antagonism is advanced as a plausible contributor to IBO’s anti-withdrawal effects. Neurotrophic factors and plasticity: Both IBO and NOR induce expression of GDNF and BDNF in vitro and in vivo. The roles of these neurotrophic factors in addiction are complex and region- and context-dependent: they can both facilitate and inhibit drug‑taking behaviours depending on drug type, brain locus and timing. NOR—but not IBO—was reported to increase dendritic arbor complexity with an EC50 comparable to ketamine; this plasticity effect was partially blocked by a 5-HT2A antagonist, implicating some serotonergic mediation despite low receptor affinity. Other targets: The authors note additional moderate or low-affinity interactions that may be relevant. IBO shows moderate σ2 and slight σ1 sigma receptor affinity (NOR less so); sigma receptors have been implicated in stimulant and alcohol models of addiction. Muscarinic receptors (M1–M3) show micromolar binding by IBO/NOR and might relate to autonomic effects (for example bradycardia) and possibly to psychostimulant reinforcement. IBO/NOR have low-affinity interactions across several serotonin receptor subtypes that may modulate wider pharmacodynamics. Transporters and efflux proteins: The review highlights a speculative but potentially important inhibitory action of IBO on ABC transporters—P‑glycoprotein (P‑gp) and breast cancer resistance protein (BCRP)—which mediate drug efflux at the blood–brain barrier and are upregulated with tolerance. Inhibition of these transporters could increase brain exposure to opioids like methadone and contribute to reduced tolerance and altered detoxification dynamics, but direct evidence for IBO’s in vivo effects on P‑gp/BCRP and clinical relevance remains to be established. Safety signals and pharmacokinetics: Human pharmacokinetic data show IBO half-life varying by dose and population (reported 2–7 h in different settings) and NOR having a substantially longer half-life (reported up to tens of hours depending on dose). Both IBO and NOR inhibit hERG channels and can delay ventricular repolarisation, accounting for QT prolongation; NOR’s comparable hERG potency combined with its longer half-life may explain persistent QT effects seen in case reports. An open-label trial reported clinically relevant QT prolongation in a sizeable fraction of patients, but the review notes methodological concerns (for example QT correction methods and concomitant CYP2D6 inhibitors) that complicate interpretation. Synthesis: Across targets, the review emphasises that IBO/NOR produce a pattern of multi-target, generally low-to-moderate affinity interactions rather than a single high-affinity ‘‘magic bullet’’ mechanism. The authors collate evidence that combined actions on KOR, MOR (antagonism), DAT/VMAT2, SERT, NMDA receptors, nAChRs, NTF induction and possible ABC transporter modulation could act synergistically to reduce drug reward, attenuate withdrawal, lower tolerance and provide antidepressant effects, but causal links remain incompletely established.

Ona and colleagues interpret the assembled evidence through a polypharmacology lens: rather than seeking a single dominant receptor, they argue IBO’s putative anti-addictive effects are best understood as emergent properties of weak-to-moderate perturbations across multiple targets. The review highlights plausible synergies—for example, SERT inhibition, NMDA antagonism and induction of neurotrophic factors may all contribute to antidepressant and anti-withdrawal effects; KOR agonism and DAT/VMAT2 actions may jointly modulate dopaminergic reward pathways; and inhibition of β‑arrestin‑2 recruitment together with NMDA antagonism and potential P‑gp/BCRP inhibition could reduce tolerance and facilitate detoxification. The authors position these conclusions relative to prior work by noting that much earlier literature sought ‘‘key targets’’ with selective ligands, an approach they consider limited for a multi-target natural product. They call for modern, system-level methods—omics and comprehensive multi-target profiling—to capture the complex molecular landscape affected by IBO/NOR and to inform rational design of safer, multi-target therapeutics. Specific research recommendations include more detailed receptor binding and pharmacokinetic characterisation at therapeutically relevant doses, human neuroimaging studies to map in vivo neuropharmacology, and preclinical omics-based studies to clarify downstream molecular cascades. Acknowledged limitations and uncertainties are explicit: the clinical evidence base lacks adequately powered randomised controlled trials; mechanistic data are heterogeneous and sometimes contradictory across models, doses and brain regions; the precise roles of neurotrophic factors (BDNF, GDNF) are context-dependent and unresolved; and some proposed mechanisms—such as ABC transporter inhibition—remain speculative. Safety concerns, especially cardiotoxicity via hERG inhibition and QT prolongation, are reiterated as major impediments to clinical translation and motivate the search for non‑toxic analogues. Finally, the review notes a paucity of contemporary data on subjective experiences elicited by IBO using standardised psychometric tools, despite anecdotal reports of vivid visionary and autobiographical phenomena that may shape psychological outcomes. The authors refrain from strong clinical claims, instead advocating for targeted preclinical and clinical work to dissect mechanisms, quantify safety risks, and leverage polypharmacology to design multi-target compounds with improved therapeutic indices.