Psychedelic 5-methoxy-N,N-dimethyltryptamine: metabolism, pharmacokinetics, drug interactions, and pharmacological actions

Pharmacology and toxicology: 5-MeO-DMT produces rapid-onset psychedelic effects in humans after inhalation or insufflation, with subjective effects beginning within minutes and generally resolving within about an hour for non‑oral routes. In experimental animals it provokes a range of behavioural and physiological responses (ataxia, mydriasis, tremor, convulsion, changes in locomotion and thermoregulation) that implicate serotonergic mechanisms. Unlike many classical hallucinogens that act predominantly via 5-HT2A, 5-MeO-DMT shows stronger affinity for 5-HT1A receptors (Ki < 10 nM) and elicits discriminative stimulus effects largely attenuated by 5-HT1A antagonists; nonetheless, 5-HT2A receptors appear to contribute to some stimulus components and to certain combined‑drug effects. Additional actions reported include inhibition of 5-HT reuptake (IC50 comparable to some psychostimulants) and potent stimulation of G‑protein binding (EC50 ≈ 100 nM, roughly 115% of the maximal activation by 5-HT). Metabolism and biotransformation: Across species, MAO-A-mediated oxidative deamination is the principal route of 5-MeO-DMT clearance. Radiolabelled rat studies identified 5-methoxyindoleacetic acid (5-MIAA) as the major urinary metabolite (54%), followed by 5-hydroxy-N,N-dimethyltryptamine glucuronide (23%), 5-hydroxyindoleacetic acid (5-HIAA, 14%) and bufotenine (9%), indicating that oxidative deamination and O-demethylation are dominant pathways. Human in vitro work and CYP2D6-humanised mouse models support the conclusion that O-demethylation to bufotenine is catalysed predominantly by CYP2D6, while MAO-A remains the main inactivation pathway. The CYP2D6.10 allelic isoform showed markedly reduced activity compared with wild-type CYP2D6.1 in forming bufotenine, and human hepatocytes lacking CYP2D6 activity failed to produce bufotenine in vitro. Pharmacokinetics: In rodents 5-MeO-DMT is rapidly absorbed and cleared; after intraperitoneal dosing in mice Cmax occurs at about 5–7 minutes and terminal half-life is short (12–19 minutes). The compound is lipophilic (oil/water partition coefficient 3.30) and distributes widely, accumulating in liver, kidney and brain; in one report brain concentrations were ~1.7-fold higher than blood at 45 minutes and drug was detectable across multiple brain regions. Bufotenine formed from 5-MeO-DMT attains Cmax at ~13 minutes in mice and has an apparent half-life near 25 minutes, but systemic exposure (AUC) to bufotenine produced endogenously was reported as less than 10% of parent 5-MeO-DMT in mice. Independent human infusion data for bufotenine show rapid urinary elimination, with 68–74% of recovered radioactivity accounted for by deaminated metabolite 5-HIAA and only 1–6% as unchanged bufotenine, reflecting efficient MAO‑A clearance. Drug–drug interactions with harmaline (MAOI): Co‑exposure to MAO-A inhibitors substantially alters 5-MeO-DMT pharmacokinetics and pharmacodynamics. In vitro co‑incubation with harmaline in human hepatocytes nearly abolished 5-MeO-DMT depletion and reduced intrinsic clearance by over 24-fold. In mice, harmaline pretreatment decreased 5-MeO-DMT clearance by 4.4-fold, producing a corresponding 4.4-fold increase in systemic exposure. Inhibition of deamination shifts metabolism toward O-demethylation and increases bufotenine formation; in CYP2D6 extensive metaboliser hepatocytes bufotenine formation rose when 5-MeO-DMT was co‑incubated with harmaline. In vivo, bufotenine Cmax and AUC increased approximately 2.6- and 6-fold, respectively, after harmaline pretreatment in mice. Harmaline itself is a potent MAO-A inhibitor and a serotonergic agonist, and its combined pharmacokinetic and pharmacodynamic effects with 5-MeO-DMT produce potentiated behavioural responses (for example, biphasic effects on locomotion and enhanced hyperthermia) and have been linked to severe or fatal serotonin toxicity in animals and reported human intoxication cases. Role of CYP2D6 polymorphism: CYP2D6 genetic variability substantially influences bufotenine formation from 5-MeO-DMT and modifies harmaline pharmacokinetics. Correlations were found between 5-MeO-DMT O‑demethylation and CYP2D6 activity in human liver microsomes when MAO was inhibited. CYP2D6 allelic isoforms differed in catalytic activity (CYP2D6.1, CYP2D6.2, CYP2D6.10), with CYP2D6 poor metaboliser hepatocytes producing no bufotenine. In Tg‑CYP2D6 mice, systemic exposure (AUC) to bufotenine after 5-MeO-DMT dosing was higher than in wild-type mice; after co‑administration with harmaline the systemic bufotenine exposure was ~24% of that to 5-MeO-DMT in Tg mice versus ~15% in wild-type mice, indicating an effect of CYP2D6 status on the magnitude of the interaction. Harmaline depletion was about 2.5 times slower in human CYP2D6 poor metaboliser hepatocytes than in extensive metaboliser hepatocytes, and animal studies showed CYP2D6 status also affected harmaline-induced hypothermia and other pharmacodynamic readouts.

Shen and colleagues interpret the assembled evidence to indicate that 5-MeO-DMT is a rapidly acting psychoactive tryptamine whose principal metabolic clearance is MAO-A-mediated deamination, while a smaller, CYP2D6-dependent O-demethylation pathway produces the active metabolite bufotenine. Because bufotenine has relatively higher 5-HT2A affinity and 5-MeO-DMT shows strong 5-HT1A activity, the clinical and behavioural profile of 5-MeO-DMT may reflect a combination of parent- and metabolite-mediated receptor effects. The review emphasises that co‑administration with MAO-A inhibitors such as harmaline both increases parent drug exposure by blocking deamination and diverts 5-MeO-DMT toward CYP2D6-dependent O-demethylation, thereby raising bufotenine levels; these pharmacokinetic changes combine with the independent serotonergic actions of harmaline to produce potentiated responses and increase the risk of hyperserotonergic toxicity. The authors position these mechanistic conclusions against prior reports of severe animal toxicity and documented human intoxication cases involving combined tryptamine–MAOI use. They also highlight that wide interindividual variability in CYP2D6 (more than 90 allelic variants) can alter the balance between parent drug and active metabolite, and may therefore modulate both therapeutic or psychoactive intensity and toxicity risk. The extracted text does not present a dedicated limitations section or detail systematic search methods for the literature reviewed, so the authors do not explicitly enumerate methodological limitations of their review or of the individual studies beyond noting species differences and the contribution of multiple enzymes to metabolism. The main implications discussed are clinical and toxicological: combined use of 5-MeO-DMT and MAOIs can be dangerous, CYP2D6 genotype may serve as an informative marker for bufotenine production during such interactions, and understanding both pharmacokinetic and pharmacodynamic components is necessary to assess intoxication risk and interpret variable responses.

The paper concludes that 5-MeO-DMT is a natural, fast-acting psychoactive tryptamine predominantly cleared by MAO-A deamination, with a minor CYP2D6-mediated pathway producing the active metabolite bufotenine. Co‑use with MAO-A inhibitors such as harmaline markedly elevates and prolongs exposure to both 5-MeO-DMT and bufotenine and, together with harmaline’s serotonergic actions, can precipitate severe or fatal serotonin toxicity. CYP2D6 genetic variability influences bufotenine formation and harmaline disposition and thus may help predict individual susceptibility to enhanced effects or intoxication during combined use.