4-OH-DiPT

Origins:
a psilocin the body cannot hold onto

4-OH-DiPT is psilocin with both N-methyl groups swapped for isopropyls. That one substitution is the whole story: it preserves 5-HT_2A agonism almost intact while changing how long the molecule survives in a human being.

It entered the literature in 1977, when David Repke, W. J. Ferguson and D. K. Bates published the first of a series titled simply Psilocin analogs — a synthesis paper on 3-[2-(dialkylamino)ethyl]indol-4-ols, with no pharmacology attached.¹ The compound was a structural exercise. Its human characterisation came from Alexander Shulgin, recorded in his lab books by 1980 and published in 1997 as entry #17 of TiHKAL.^2,3

Shulgin reported an oral dose range of 15–20 mg and a duration of 2–3 hours, with onset at 15–20 minutes and peak effects at 20–30.² He also flagged what remains the compound's most awkward property: an exceptionally steep dose–response curve. Below 10 mg he found few or no effects; above 20 mg he did not go, because of the intensity of what he had already met. Twenty milligrams produced a plus-three on his own scale that, in his phrase, flirted with the plus-four transcendental peak.² Later analysis of user reports gives a wider practical window of 3–30 mg,⁴ which does not so much contradict Shulgin as illustrate the problem: the useful range is narrow and the cliff is close.

The reported subjective profile deserves attention, because it is not simply psilocybin in miniature. Accounts describe introspective shift, insight and realisation, mild object distortion, rainbow halos and slight colour effects — but very little closed-eye imagery and little in the way of psychedelic visuals generally. Alongside that: mild stimulation, mild elation, light tension, orgasmic enhancement, and powerful religious-flavoured experience. The recurring physical complaints are leg tremor, chill sensations, muscle loosening and a vague body malaise.² A largely non-visual, insight-forward, strongly noetic experience is an interesting foundation on which to build an anxiolytic.

Shulgin himself doubted it was pharmacologically distinctive. Writing about the ethyl homologue 4-HO-MET, he suspected that neither it nor “the isopropyl homologue 4-HO-DIPT for that matter, could be distinguished from the methyl counterpart psilocin in any blind clinical study.”⁵ The modern development thesis does not dispute this. It depends on it: the claim is a psilocin-equivalent experience delivered in half the time, not a better one.

A drug that never had a scene

The most striking sociocultural fact about 4-OH-DiPT is how little sociocultural history it has. It has no bath-salts era, no moral panic, no branded packaging, no cluster of emergency-department presentations. It is a compound that was published, tried by a handful of people, sold thinly online, and largely left alone.

It was first recorded as a novel designer drug in Europe in 2005, in the EMCDDA–Europol annual reporting under Council Decision 2005/387/JHA.⁷ Thereafter it remained, in the standard description, relatively uncommon and occasionally distributed on the online research chemical market — with very little known about its pharmacology, metabolism or toxicity in humans, and a limited history of human use.⁹ That characterisation, written for a harm-reduction audience, is also an accurate summary of the evidence base a sponsor inherited.

Where 4-OH-DiPT does have a cultural position, it is inside psychedelic subculture rather than the drug market: it belongs to the Shulgin canon. TiHKAL made it legible to a generation of chemists and self-experimenters, and its reputation there is specific — extremely fast, extremely short, and easy to overshoot. It has been described in that literature as a plausible “novice” introduction to hallucinogens on account of the brevity,² a framing that sits oddly next to the steep dose–response curve and is best treated as folklore rather than guidance.

The one place the compound became briefly, unusually public was in a regulatory proceeding — and it is a story about researchers and industry, not users. That is Section III.

The rule that was withdrawn

In January 2022 DEA published a Notice of Proposed Rulemaking to place five tryptamine hallucinogens in Schedule I: 4-OH-DiPT, 5-MeO-AMT, 5-MeO-MiPT, 5-MeO-DET and DiPT.¹⁰ Eighteen months later the compound was still unscheduled, and the reason is one of the more instructive episodes in recent psychedelic drug policy.

The administrative record is old. DEA gathered its data and submitted it to HHS on 19 December 2008; HHS returned scientific and medical evaluations with scheduling recommendations on three dates in 2012. The 2022 rule rested on those 2012 evaluations, and asserted that the five substances share structural and pharmacological similarities with scheduled tryptamines including DMT, 5-MeO-DiPT and psilocin, and have no approved medical use in the United States.¹⁰ A ten-year-old evidence review was thus proposed as the basis for permanent control.

The response was atypical. DEA received nearly 600 comments, most opposing, and four hearing requests.^11,12 A hearing was scheduled; ALJ Teresa Wallbaum issued an order setting the process in motion.¹² Petitioners attacked the staleness of the record and the class-level reasoning — in particular the claim that hallucinogen users may develop psychological dependence, which the animal literature tends to contradict, and the reliance on drug-discrimination studies to establish abuse liability.¹³ Matthew Johnson's submission put the availability question directly: it could not reasonably have been concluded in 2012, and certainly not ten years later, that 4-OH-DiPT was readily available to be abused or actually being diverted.¹³

On 27 July 2022 DEA withdrew both the proposed rule and the notice of hearing, cancelled the hearing, and terminated the proceedings — stating that on further consideration it was appropriate to submit a new request to HHS for an updated scientific and medical evaluation and scheduling recommendation. The withdrawal notice adds, plainly, that DEA may issue a new proposed rule in future if warranted.¹⁴

The practical read for a development programme: unscheduled status materially eases manufacturing, shipping, site licensing and multi-site trial logistics relative to a Schedule I asset — this is the operational advantage over psilocybin, and over methylone. It is also revocable by a single agency action on an evidentiary review that DEA has already said it intends to refresh. Any programme plan should carry a rescheduling contingency.

Mechanism of action

4-OH-DiPT is a non-selective serotonin receptor agonist, acting at 5-HT_2A and 5-HT_2B among others, and it produces the head-twitch response in rodents — the standard behavioural proxy for a psychedelic 5-HT_2A agonist.^6,16,17,18 There is no exotic mechanism here and the sponsor does not claim one. What is interesting sits in the off-target columns and in the kinetics.

The 5-HT_2C question

Across four independent in vitro characterisations — Rickli 2016, Klein 2021, Kozell 2023 and Glatfelter 2023 — 4-OH-DiPT emerges as having far lower potency at 5-HT_2C than at 5-HT_2A, unlike many psychedelic tryptamines.^16,17,18,19 If that holds it is therapeutically relevant: 5-HT_2C agonism is associated with anxiogenesis and appetite suppression, and a 5-HT_2A-biased profile is a plausible route to a better-tolerated acute experience.

It should not be treated as settled. Kelly et al. 2024 found only about 2.5-fold greater potency at 5-HT_2A than 5-HT_2C.²⁰ Four studies pointing one way and one pointing another, across different expression systems and functional readouts, is a methodological disagreement rather than a resolved fact.

Secondary and absent activities

• No rodent TAAR1 binding. Unlike many tryptamines, 4-OH-DiPT is not a ligand at rodent trace amine-associated receptor 1.^16,21 TAAR1 modulates the head-twitch response to some serotonergic agents,²² so its absence simplifies interpretation of preclinical behaviour.
• Possible serotonin reuptake inhibition, with potency that varies substantially across studies — reported but not reliably quantified.^16,17,18,19
• 5-HT_2B agonism is present. This is the standard valvulopathy-adjacent flag for the tryptamine class. Single-administration dosing makes it a far smaller concern than it would be for a chronic agent, but it is a real entry on the safety ledger and the published RE104 work characterises 5-HT_2B binding explicitly.^8,16

The prodrug is the invention

4-OH-DiPT's own liability is a 4-hydroxy group vulnerable to first-pass metabolism and oxidation — the same problem psilocybin solves with a phosphate ester. RE104 solves it with a glutarate hemiester. Bryson et al. 2024 report that cleavage in plasma was rapid (<30 min) and essentially complete (>95%) at 37 °C, that 4-OH-DiPT appears quickly in plasma after subcutaneous RE104, and that the half-life of the active drug in rats was 40 minutes.⁸ Reported binding for the active drug at 5-HT_2A was IC₅₀ 1.5 × 10⁻⁷ M, K_i 1.2 × 10⁻⁷ M; the prodrug itself binds far more weakly (K_i 4.3 × 10⁻⁶ M), which is what a prodrug should look like.⁸ Crucially, plasma 4-OH-DiPT concentration tracked head-twitch intensity in rats, establishing a PK–PD relationship.⁸

Subcutaneous administration also removes gastrointestinal variability, which for a compound with this dose–response steepness is arguably as important as the ester. The 1996-era objection to 4-OH-DiPT as a medicine was that you could not dose it reliably. The prodrug plus the injection route is the answer to that objection.

Caveat. Published EC₅₀ and E_max values for 4-OH-DiPT span wide ranges across expression systems and functional readouts — at some targets by more than an order of magnitude. No single lab has profiled 4-OH-DiPT, psilocin and the therapeutic comparators side by side under one assay. These bars are our reading of the direction of difference across sources 16–20, not a harmonised dataset. Treat the 5-HT_2C row in particular as an open question.

Preclinical research, and the anxiety case

For the RECLAIM indication, one paper carries most of the weight — and it is not a Reunion paper.

The convergence with the methylone literature is worth naming explicitly, because it is not coincidence. Two structurally unrelated compounds — a β-keto amphetamine and a 4-hydroxytryptamine — are both being developed for trauma- and anxiety-spectrum indications on the strength of fear-extinction enhancement. Extinction learning has become the field's shared translational endpoint, and amygdala excitability its shared substrate. For a GAD programme that is encouraging (the mechanism is not idiosyncratic to one chemotype) and cautionary (the endpoint's predictive validity for chronic worry, as opposed to cued fear, is not established).

Two further preclinical threads are worth logging. Flanagan et al. 2021 found 4-OH-DiPT to have fully efficacious anti-inflammatory effects in a rat model of asthma, as part of a structure–activity analysis identifying the anti-inflammatory pharmacophore of psychedelics²³ — an indication direction nobody is currently pursuing for this compound. And Halberstadt et al. 2020 placed it within the mouse head-twitch potency series used to predict human hallucinogenic potency,²⁴ which is where its rodent potency figures come from.

On toxicology, the honest statement is that there is very little. There is no published repeat-dose neurotoxicity programme, no dedicated cardiovascular safety study of 4-OH-DiPT in the public literature, and no human abuse-potential study. The comparison with methylone is stark: methylone has a decade of contested but substantial toxicology; 4-OH-DiPT has almost none, in either direction.

Prior development, and the IP position

Unlike methylone, 4-OH-DiPT was never patented as a medicine in the twentieth century. Repke's 1977 paper was pure synthetic chemistry. Shulgin never filed on it. There is no record of a 1990s antidepressant claim, no abandoned pharma programme, no veterinary application. From 1977 to 2021 the compound has no pharmaceutical development history at all.

This is a cleaner starting position than it may appear. Because there is no old composition-of-matter patent, the molecule is unencumbered; because it was never developed and failed, there is no adverse regulatory history to explain. The corollary is that the molecule is also unprotectable, and so the entire IP position rests on the prodrug.

The corporate history is compressed. Field Trip Psychedelics developed the prodrug as FT-104 and announced first human dosing in July 2022.²⁷ In August 2023 Reunion Neuroscience — Field Trip's successor entity — was acquired by MPM BioImpact and taken private.²⁸ A Series A co-led by MPM BioImpact and Novo Holdings followed in 2024 at $103 M, upsized to $133 M in September 2025 when a $30 M tranche triggered on the RECONNECT efficacy result.^29,30 The compound was renamed luvesilocin ahead of registration.³¹

Reunion is also advancing RE245, described as a non-psychedelic serotonergic neuroplastogen intended to deliver 5-HT_2A-mediated neuroplasticity without hallucinations or cardiotoxicity, with an IND planned for 2026 and Phase 1 in 2027.³² Worth tracking as a hedge: if the non-psychedelic thesis works, the clinic-hours advantage that justifies luvesilocin narrows considerably.

The clinical programme

Phase 1

Ludbrook, Bryson, Taylor, Hocevar-Trnka, Johnson, Hirman et al., published in the Journal of Clinical Psychopharmacology in 2025, was a double-blind, randomised, single-ascending-dose, placebo-controlled study of subcutaneous RE104 across 5 to 40 mg — roughly 4–32 mg of 4-OH-DiPT equivalent.³³ The active metabolite appeared rapidly in plasma, and peak levels correlated with drug effect on the modified DEQ and with MEQ scores. RE104 produced a psychedelic state similar in intensity and quality to psilocybin. There was no increase in suicidality on the C-SSRS, and MOAA/S alertness remained largely normal at all timepoints regardless of dose. A single 30 mg subcutaneous dose was selected as the therapeutic dose on safety, tolerability and pharmacodynamic grounds.^33,34 A separate lactation study in 14 healthy lactating volunteers (NCT06659263) characterised elimination and transfer into breastmilk — a necessary study for a PPD indication, and a good sign of programme discipline.³⁴

RECONNECT — Phase 2, postpartum depression

RECONNECT (NCT06342310) was multicentre, randomised, double-blind, parallel-group and active dose-controlled: 84 adult female patients with moderate-to-severe PPD (HAMD-17 ≥ 24), randomised to a single subcutaneous 30 mg dose of RE104 or a subperceptual 1.5 mg dose. The primary endpoint was change from baseline in total MADRS at Day 7.³⁵

The trial met it: a 23.0-point MADRS total score reduction at Day 7 in the 30 mg arm (p = 0.0094), with clinically meaningful reductions from the first day after administration and maintained through the 28-day follow-up. Response and remission rates and other symptom measures also improved, alongside HAM-A, CGI-I and the Barkin Index of Maternal Function.³⁵ Reunion has since completed an End-of-Phase-2 meeting with FDA and reports agreement that a single successful Phase 3 would complete the registration package.³⁵

RECLAIM — Phase 2, generalized anxiety disorder

RECLAIM is a multicentre, randomised, double-blind, dose-controlled Phase 2 trial of RE104 in adults with GAD. The primary endpoint is change in Hamilton Anxiety Scale (HAM-A) from baseline at Week 4; safety and tolerability are also assessed.^29,36 It was funded out of the upsized Series A and slated to begin in Q1 2026.^29,31

The indication logic is straightforward. GAD is estimated to affect 6.8 million US adults annually, about 3.1% of the adult population; standard care is SSRIs, SNRIs and CBT, and roughly half of patients fail to respond to initial pharmacotherapy, with a majority never achieving remission on available therapies.^29,30 Untreated GAD raises the risk of secondary MDD, other anxiety disorders and suicide.²⁹

Two things to watch. First, HAM-A at Week 4 after a single dose is an ambitious endpoint for a chronic, trait-like condition — the PPD and AjD indications both involve an acute precipitant, and GAD does not. Second, the preclinical anxiety evidence is fear-extinction and cued-fear based; the translational distance from cued fear to generalised worry is the programme's main scientific risk, and it is larger here than in AjD.

Regulatory position

FDA granted Breakthrough Therapy designation to luvesilocin on 23 February 2026.³¹ A pivotal Phase 3 in PPD is planned for 2026; REKINDLE (NCT07002034) in adjustment disorder in cancer and other medical illnesses is enrolling, with topline expected in Q1 2027.^31,32,36 Note the sequencing risk for RECLAIM: PPD is the registrational path, and GAD sits behind both PPD and AjD in the queue for capital and attention.

Where 4-OH-DiPT sits in the commercial landscape

Luvesilocin enters a crowded field. A dozen psychedelic and psychedelic-adjacent programmes were in Phase 2 or Phase 3 as of August 2026 — and 4-OH-DiPT is one of the few whose differentiation is primarily kinetic rather than mechanistic.

Three things follow for the RECLAIM programme. On competition: in GAD specifically the field is thin — MM120 is the only other serious contender and it is a Phase ahead, while Cybin's CYB004 is at the same stage. On differentiation: the ~3.6-hour session is real but no longer unique; BPL-003, GH001, VLS-01 and CYB003 are all engineered for short clinic time, so “shorter than psilocybin” is now table stakes rather than a moat. On regulatory position: 4-OH-DiPT's unscheduled status is genuinely distinctive — every other compound in this table is Schedule I — and it is the differentiator least likely to be competed away, though it is also the one revocable by a single DEA action.

Established · A

• It is a psilocin homologue and a 5-HT_2A agonist producing head-twitch in rodents.^16,17,18,19
• Oral duration is 2–3 h with 15–20 min onset — among the shortest of orally active psychedelics.^2,6
• Synthesised 1977; human-characterised by Shulgin; no pre-2021 pharmaceutical development.^1,2
• Federally unscheduled in the US; DEA proposed and withdrew Schedule I in 2022.^10,14
• RE104 cleaves rapidly and near-completely to 4-OH-DiPT.⁸

Probable · B

• It enhances fear extinction and increases GABAergic inhibition of BLA principal neurons.²⁰
• It is anxiolytic in rodents.²⁰
• It is not a rodent TAAR1 ligand — reported by two groups.^16,21
• A single 30 mg s.c. dose reduces MADRS vs a subperceptual comparator at Day 7 in PPD.³⁵
• The subjective experience is psilocybin-like in intensity and quality but markedly less visual.^2,33

Speculative · C

• The 5-HT_2A-over-5-HT_2C selectivity claim. Four studies support it; Kelly finds only ~2.5-fold.^16,20
• Efficacy in GAD. No human anxiety-disorder data exist; RECLAIM has not reported.²⁹
• Durability past 28 days from a single dose.³⁵
• That the abbreviated experience is therapeutically equivalent, not merely subjectively similar. Untested directly.
• Anti-inflammatory potential as a second indication direction.²³