DOI

DOI (2,5-dimethoxy-4-iodoamphetamine) is a substituted phenethylamine and amphetamine derivative of the DOx family and one of the most extensively characterized serotonergic psychedelic agents in the preclinical pharmacology literature. First described by Coutts and Malicky in 1973 and subsequently documented in detail by Alexander Shulgin in PiHKAL (1991), DOI has become the prototypical 5-HT2A/2C receptor agonist in neuroscience research, owing to its high affinity and selectivity for the 5-HT2 receptor family (Ki at 5-HT2A approximately 0.5 to 3 nM in rat cortical membranes), its availability as a radioiodinated probe ([125I]-DOI) for receptor autoradiography and binding assays, and its robust induction of the head-twitch response in rodents, the standard behavioral proxy for hallucinogenic 5-HT2A agonism.

The pharmacology of DOI extends substantially beyond its role as a psychedelic reference compound. The (R)-enantiomer, (R)-DOI, demonstrates extraordinary anti-inflammatory potency, blocking tumor necrosis factor alpha (TNF-alpha)-induced inflammation in rat aortic smooth muscle cells with an IC50 of approximately 15 picomolar, a potency several orders of magnitude greater than conventional non-steroidal or steroidal anti-inflammatory agents. In vivo, (R)-DOI at doses of 0.01 to 0.3 mg/kg (well below the threshold for behavioral detection in drug discrimination assays) completely blocks TNF-alpha-induced proinflammatory gene expression in the murine small intestine and circulating interleukin-6, effects confirmed as 5-HT2A receptor-dependent by reversal with the selective antagonist M100907. These findings have prompted investigation of (R)-DOI in allergic asthma models, where inhaled doses of 0.01 mg/kg prevent airway hyperresponsiveness, eosinophilia, mucus hyperproduction, and pulmonary inflammation in ovalbumin-sensitized mice.

DOI also exhibits psychoplastogenic activity. In cultured cortical neurons, DOI at low-micromolar concentrations increases neuritogenesis, dendritic arbor complexity, spine density, and synaptogenesis through 5-HT2A receptor-dependent activation of TrkB, mTOR, and CREB signaling pathways, promoting the transcription of plasticity-associated genes including Arc, Bdnf1, Cebpb, cFos, and Egr2. These structural neuroplasticity effects are shared with other serotonergic psychedelics (psilocin, LSD, DMT) and are the molecular basis for the emerging psychoplastogen therapeutic concept.

Recent preclinical work (2019 to 2025) has extended DOI research into substance use disorder models. (R)-DOI dose-dependently reduces cocaine self-administration and cocaine-conditioned place preference in rats through 5-HT2A receptor mechanisms, reduces voluntary ethanol consumption in mice, and attenuates heroin motivation in heroin-alcohol co-use models. These findings position DOI as a mechanistic probe for the broader investigation of psychedelic-assisted approaches to addiction.

DOI has no approved therapeutic indication in any jurisdiction and has not been administered to humans in formal clinical trials. Human pharmacological data derive principally from Shulgin's self-experimentation records, which report oral activity at 1.5 to 3 mg (racemic) with a duration of 16 to 30 hours. The compound is not a monoamine releasing agent and does not produce the dopaminergic stimulant profile of classical amphetamines. Metabolism proceeds principally through CYP2D6-mediated O-demethylation. DOI has historically been unscheduled in the United States, though DEA scheduling proceedings initiated in December 2023 are expected to result in Schedule I placement. This monograph reviews the chemistry, synthesis, receptor pharmacology, signaling mechanisms, preclinical pharmacology across anti-inflammatory, neuroplasticity, and substance use disorder applications, pharmacokinetics, sourcing, handling, stack interactions, safety signal, and a comparative assessment of five 5-HT2A agonist research tools against DOI on five competency standards.