4-HO-DET

# Research Output: 4-HO-DET

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## Chemical Identity

**Verified via PubChem CID 9991554** [Ref 1]:

| Field | Value | Source |
|---|---|---|
| PubChem CID | 9991554 | PubChem API (api_verified) |
| IUPAC Name | 3-[2-(diethylamino)ethyl]-1H-indol-4-ol | PubChem API |
| Molecular Formula | C₁₄H₂₀N₂O | PubChem API |
| Molecular Weight | 232.32 g/mol | PubChem API |
| InChIKey | OHHYMKDBKJPILO-UHFFFAOYSA-N | PubChem API |
| CAS Number | 22204-89-3 | WikiDoc [Ref 29], ChemicalBook (web_retrieved) |
| SMILES | Not returned by PubChem API — gap; structural derivation suggests CCN(CC)CCc1c[nH]c2cccc(O)c12 but requires API verification |  |
| Melting Point | 103–104°C | TIHKAL [Ref 20] (unverifiable) |
| Physical Stability | Air-sensitive; discolors rapidly in presence of oxygen | TIHKAL [Ref 20] |
| Storage | Requires inert atmosphere at −30°C | TIHKAL [Ref 20] |

**Seed data cross-check:**
- The brief's IUPAC name, chemical class, and formula fields are consistent with verified data.
- SMILES and PubChem CID were blank in the brief — both now confirmed (CID 9991554; SMILES gap flagged below).
- The InChIKey was blank in the brief — now verified: OHHYMKDBKJPILO-UHFFFAOYSA-N [Ref 1].

**Structural context:** 4-HO-DET is the N,N-diethyl homolog of psilocin (4-HO-DMT). It shares the 4-hydroxyindole pharmacophore responsible for 5-HT2A agonism and differs from psilocin only in the substitution of two ethyl groups for two methyl groups on the terminal amine. It is structurally distinct from its presumed prodrug ethocybin (4-phosphoryloxy-DET; CEY-19), which requires enzymatic dephosphorylation to become active.

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## Pharmacology

### Primary Mechanism of Action

4-HO-DET acts as a non-selective serotonin receptor agonist with primary activity at the 5-HT₂A receptor. By structural analogy to psilocin and via in vivo evidence, it also engages 5-HT₁A and 5-HT₂C receptors (Nichols DE 2018 [Ref 12]; Halberstadt et al. 2011 [Ref 14]).

The 4-hydroxy group on the indole ring is the key pharmacophore for 5-HT₂A agonism. Unlike its prodrug ethocybin (4-phosphoryloxy-DET), 4-HO-DET is directly active without requiring enzymatic conversion, as the free phenol binds directly at serotonin receptors (Nichols DE 2018 [Ref 12]).

### Receptor Binding Data

**No published Ki or EC₅₀ values specific to 4-HO-DET were identified in the peer-reviewed literature.** The following data are from closely related sources:

- **In vivo hallucinogen-like activity (rat):** Gatch, Hoch & Carbonaro (2021) [Ref 5] directly tested 4-OH-DET in male Sprague-Dawley rats trained to discriminate DOM (a 5-HT₂A agonist) from saline. 4-OH-DET **fully substituted** for DOM's discriminative stimulus. 4-hydroxy compounds in this study were uniformly more potent than their 4-acetoxy counterparts. This constitutes the clearest published in vivo evidence of 5-HT₂A-mediated hallucinogen-like activity for 4-HO-DET.

- **Receptor binding screen (diethyl variant included):** Glatfelter et al. (2023) [Ref 23] examined receptor binding profiles of tryptamine psychedelics with varying 4-position substituents (hydroxy, acetoxy, propionoxy) and N,N-dialkyl substitutions explicitly including **dimethyl, methyl-ethyl, diethyl**, methyl-propyl, ethyl-propyl, diisopropyl, methyl-allyl, and diallyl variants. The 4-hydroxy, N,N-diethyl compound (4-HO-DET) is therefore included in this binding screen. Key findings: tryptamine psychedelics target multiple serotonin receptors including 5-HT₁A; differential binding profiles observed across alpha receptors, dopamine receptors, histamine receptors, and SERT with N,N-dialkyl variation. Specific Ki values for 4-HO-DET were not recoverable from the abstract; full paper was not accessible.

- **DET (parent compound) 5-HT₂A functional activity:** Rabin et al. (2002) [Ref 6] demonstrated that N,N-diethyltryptamine (DET, the non-hydroxylated parent) causes concentration-dependent stimulation of phosphoinositide hydrolysis via 5-HT₂A receptors in PC12-5-HT₂A cells. This establishes the pharmacological activity of the N,N-diethyl scaffold at 5-HT₂A.

- **Psilocin analog receptor pharmacology:** Halberstadt et al. (2011) [Ref 14] demonstrated that psilocin (4-HO-DMT, the closest structural analog) acts as an agonist at 5-HT₁A, 5-HT₂A, and 5-HT₂C receptors in mice. The 5-HT₂A receptor mediates the head twitch response (hallucinogen marker); 5-HT₁A mediates locomotor depression; 5-HT₂C modulates path linearity. By structural analogy, 4-HO-DET is expected to share this multi-receptor profile.

- **SAR for 4-hydroxyindole tryptamines:** Gerasimov et al. (1999) [Ref 28] established that rigid pyrrolidine analogs of psilocin bind to 5-HT₂A with comparable affinity to psilocin and produce LSD-like hallucinogenic effects in drug discrimination paradigms, confirming that the 4-hydroxyindole scaffold is the primary determinant of 5-HT₂A activity and hallucinogen-like effects.

- **5-HT₁A modulation of 5-HT₂A-mediated effects:** Shahar et al. (2022) [Ref 31] confirmed that 5-HT₁A agonism inhibits 5-HT₂A-mediated head twitch response. Glatfelter et al. (2023) [Ref 23] showed that 5-HT₁A-mediated hypothermia and hypolocomotion emerge at higher doses of tryptamine psychedelics when 5-HT₁A activity dominates. This is relevant to interpreting dose-dependent effects of 4-HO-DET at higher dose ranges.

**⚠️ FLAG FOR REVIEW:** No substance-specific Ki or EC₅₀ values for 4-HO-DET at any receptor were found in the peer-reviewed literature. All receptor binding claims rely on class analogy or studies that include 4-HO-DET without extractable compound-specific values.

### Pharmacokinetics

**No human pharmacokinetic data specific to 4-HO-DET has been published.**

The following data are from psilocin (4-HO-DMT), the structurally closest analog with published human PK:

- **Oral bioavailability:** ~52.7 ± 20% for psilocin derived from oral psilocybin (Hasler et al. 1997 [Ref 19]; Meshkat et al. 2025 [Ref 18])
- **Tmax:** 1.8–4 hours after oral psilocybin administration (Meshkat et al. 2025 [Ref 18])
- **Elimination half-life:** 1.5–4 hours (psilocin; Meshkat et al. 2025 [Ref 18])
- **Volume of distribution:** 277–1016 L (extensive tissue distribution; psilocin; Meshkat et al. 2025 [Ref 18])
- **Primary metabolic pathway (psilocin):** CYP2D6 and CYP3A4 (primary), MAO-A (secondary). Metabolites: 4-hydroxyindole-3-acetic acid (4-HIAA) and 4-hydroxytryptophol (Meshkat et al. 2025 [Ref 18])
- **DMT CYP metabolism:** Eckernäs et al. (2023) [Ref 17] demonstrated that DMT is rapidly metabolized by CYP2D6 with formation of oxygenated indole metabolites; harmine inhibited DMT metabolism via MAO-A inhibition. This CYP2D6 involvement likely applies to 4-HO-DET given shared indole tryptamine structure.

**Important distinction:** 4-HO-DET bears a free hydroxyl group (phenol/indolol) and is directly active without prodrug conversion. This contrasts with psilocybin (phosphate ester prodrug) or ethocybin (its own prodrug), which must be dephosphorylated to release the active 4-hydroxy compound. The free phenol form is more bioavailable directly but is also more chemically labile.

**⚠️ FLAG FOR REVIEW:** All PK data for 4-HO-DET is inferred from structural analogy to psilocin and DMT. No published human or animal PK study for 4-HO-DET was found. Generation agent must not present these as confirmed 4-HO-DET PK values without appropriate qualification.

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## History

### Discovery and Early Development

4-HO-DET was synthesized by **Albert Hofmann** and **Franz Troxler** at Sandoz Pharmaceuticals (Basel, Switzerland) in the **late 1950s** as part of a broader program investigating structurally modified tryptamines for psychopharmacological activity [Ref 22, Ref 29]. The compound received the Sandoz laboratory code designation **CZ-74**. Its phosphate ester prodrug, 4-phosphoryloxy-N,N-diethyltryptamine (ethocybin), was simultaneously developed under the code **CEY-19**.

This work occurred in the immediate aftermath of Hofmann's discovery of LSD (1943) and psilocybin (1958), during a period of intense Sandoz investigation into psychopharmacological scaffolds. 4-HO-DET was among the earliest structurally modified synthetic psychedelic tryptamines developed, predating most research chemicals of the current era by decades [Ref 15].

### Clinical Research Era (1960s)

The primary human research on 4-HO-DET was conducted by **Hanscarl Leuner** and **G. Baer** in Germany during the 1960s. Leuner, the leading figure of European psycholytic therapy (Passie, Guss & Krähenmann 2022 [Ref 16]), conducted **more than 160 clinical trials** with 4-HO-DET (CZ-74), exploring its potential as an adjunct to psychoanalytically-oriented psychotherapy [Ref 20]. Leuner specifically valued the compound for its **shorter duration** compared to LSD, which allowed psycholytic sessions to be completed within a workday, and its reportedly favorable safety profile with minimal aftereffects.

Psycholytic therapy at this time was practiced across approximately 30 European clinical centers and by more than 100 outpatient psychotherapists (Passie et al. 2022 [Ref 16]), with Leuner's clinic in Germany being the primary center for 4-HO-DET research.

### Post-Clinical Era (1970s–1990s)

Following the international prohibition of psychedelic research substances in the late 1960s and early 1970s, clinical use of 4-HO-DET ceased. The compound was subsequently studied by **David Repke and colleagues** during the 1970s and 1980s in academic pharmacological context [Ref 22], though no PubMed-indexed papers specifically attributable to Repke on 4-HO-DET were identified through database searches.

**Alexander Shulgin** described 4-HO-DET as entry **#16** in his 1997 book *TiHKAL: Tryptamines I Have Known and Loved* [Ref 20], providing synthesis details, personal bioassay reports, and historical context including Leuner's clinical work. Shulgin's publication brought renewed attention to the compound and established the reference dosage and duration data that has informed subsequent community knowledge.

### Research Chemical Era (2000s–Present)

4-HO-DET has appeared on research chemical markets since the 2000s, typically sold as a free base or salt. It is analytically identified in test-purchase studies of novel synthetic tryptamines (Taschwer, Ebner & Schmid 2016 [Ref in OpenAlex search]). As of 2026, no renewed formal clinical research or registered clinical trials have been initiated for 4-HO-DET.

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## Subjective Effects

No controlled clinical studies documenting the subjective effects of 4-HO-DET have been published in the peer-reviewed literature. Available descriptions derive from:

1. Shulgin's *TiHKAL* bioassay reports [Ref 20]
2. Leuner's unpublished/non-English clinical observations referenced in TIHKAL [Ref 20]
3. Community experiential reports (not systematically analyzed for this article)

### From TiHKAL (#16) [Ref 20]

**At 15 mg (indolol form):** Onset within 30–45 minutes; altered time perception; visual effects; "a touch of sadness"; absence of erotic effects. Described as relatively mild.

**At 15 mg (phosphate ester/ethocybin form):** "Cosmic tenderness, infinite love, penetrating peace" with "unspeakable awe"; reports of profound emotional opening and lasting euphoria days afterward.

**At 20–25 mg (acetate form):** Body discomfort including stomach upset; body tremors; jaw tightening; anorexia; diuretic effects noted.

### General Effect Profile

Based on class pharmacology [Ref 12, Ref 14] and the discriminative stimulus profile (DOM-substitution in rats; Gatch et al. 2021 [Ref 5]), 4-HO-DET produces a psychedelic effect profile consistent with 5-HT₂A agonism: visual hallucinations, altered cognition, perceptual distortion, and emotionally significant experiences. The effects are broadly comparable to psilocin and LSD at equivalent doses.

The effects taxonomy in the database brief lists the following categories — these are consistent with the 5-HT₂A agonist psychedelic profile and supported by class-level evidence [Ref 12, Ref 14, Ref 21], though no published study has systematically catalogued these specific effects for 4-HO-DET:

- **Body:** Nasal congestion, watery eyes, stimulation, increased urination, spontaneous body sensations, motor control changes, abnormal heartbeat, yawning, temperature dysregulation, wakefulness, muscle tension, pupil dilation — all consistent with sympathomimetic/serotonergic autonomic effects
- **Perception:** External/internal hallucinations, visual tracers, drifting, color alteration, depth distortion, music enhancement — consistent with 5-HT₂A agonism in visual cortex
- **Thinking:** Thought connectivity, pattern recognition, thought loops, conceptual thinking — characteristic of serotonergic psychedelic state
- **Time/Awareness:** Time alteration, personal insight — reported across all classic psychedelic experiences

### Duration Assessment

**TIHKAL reports 4–6 hours** total duration [Ref 20]. The database brief lists **5–7 hours** total duration. These ranges overlap at 5–6 hours but diverge at their extremes.

**⚠️ FLAG FOR REVIEW:** The 5–7 hour duration in the DB is 1 hour longer at each bound than Shulgin's reported range. Leuner's clinical notes specifically cited 4-HO-DET's *shorter* duration relative to LSD as an advantage. The discrepancy may reflect: (a) higher doses used in community experience vs. Shulgin's experimental doses; (b) variant salt forms (phosphate vs. free base); or (c) individual variability. No published study resolves this discrepancy. The generation agent should propose the range most consistent with available evidence and flag this for editorial review.

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## Safety & Toxicity

### Acute Toxicity

**No published LD₅₀ data exists for 4-HO-DET in any species.** The database brief correctly notes "toxic dose is unknown." No case reports of 4-HO-DET overdose or acute poisoning were identified in PubMed, OpenAlex, or web searches.

### Adverse Effects Profile

The available adverse effect data derives entirely from TIHKAL bioassay reports [Ref 20] and clinical observations in Leuner's psycholytic sessions. Reported adverse effects at doses of 20–25 mg include:
- Gastrointestinal discomfort (stomach upset)
- Body tremors
- Jaw tension/bruxism
- Anorexia
- Diuresis/increased urination
- "A touch of sadness" at lower doses (15 mg)

Leuner reportedly noted a favorable safety profile and minimal aftereffects at clinical doses.

### HPPD Risk

Hallucinogen persisting perception disorder (HPPD) is an established risk class for 5-HT₂A receptor agonists. Litjens et al. (2014) [Ref 26] reviewed HPPD and found the majority of cases attributed to drugs with agonistic activity at 5-HT₂AR. A case of HPPD following psilocybin use (a close structural analog) was documented by Espiard et al. (2005) [Ref 27]. By class extrapolation, 4-HO-DET carries a similar HPPD risk, particularly with repeated use or at high doses.

### Psychological Risks

By analogy to other 5-HT₂A agonist psychedelics: risk of challenging or dysphoric experiences ("bad trips"), acute anxiety, dissociation, and, in vulnerable individuals, triggering of latent psychotic disorders. These risks are documented in the psilocybin literature [Ref 16, Ref 21] and apply by class extension.

**⚠️ FLAG FOR REVIEW:** All toxicological data for 4-HO-DET is based on (a) a small number of Shulgin bioassay reports; (b) Leuner's unpublished clinical observations; (c) class inference from psilocin/LSD literature. No formal toxicological study, animal LD₅₀, or clinical safety study exists in the published literature.

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## Harm Reduction

### Based on Class Evidence for 5-HT₂A Agonist Psychedelics

- **Set and setting:** Psychedelic effects are profoundly context-dependent; psychological vulnerability and environment are major determinants of outcome (class-level evidence; Passie et al. 2022 [Ref 16])
- **Start low:** Given limited published dosing data, the conservative starting dose per TIHKAL is 10 mg. The upper end of Shulgin's confirmed range is 25 mg; doses above this are unvalidated by published sources
- **Avoid combination with serotonergic drugs:** Particularly dangerous with tramadol (SERT inhibitor; Baldo 2018 [Ref 25]) and MAOIs. SSRIs may attenuate effects (Halman et al. 2024 [Ref 33])
- **Testing:** No validated colorimetric reagent profiles specific to 4-HO-DET were identified; Marquis reagent is expected to produce a dark reaction (class response for 4-HO tryptamines) but substance-specific data was not found in published sources
- **Air stability:** 4-HO-DET is documented to discolor rapidly in air [Ref 20]; storage in sealed, dark, inert-atmosphere containers is important for maintaining potency and purity
- **Emergency response:** Supportive care; benzodiazepines for agitation (standard for psychedelic adverse reactions); no specific antidote

### Contraindications (Class-Level Evidence Only)

- Personal or family history of psychotic disorders
- Concurrent MAOI use (serotonin syndrome risk)
- Concurrent tramadol use (serotonin syndrome risk; Baldo 2018 [Ref 25])
- Pregnancy (no data; class contraindication)
- Cardiovascular disease (autonomic stimulation risk)

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## Tolerance & Dependence

### Tolerance Development

Classical psychedelics including psilocin and LSD develop tolerance through **downregulation of 5-HT₂A receptors** in the frontal cortex (Buckholtz et al. 1990 [Ref 11]; de la Fuente Revenga et al. 2022 [Ref 10]). De la Fuente Revenga et al. (2022) [Ref 10] demonstrated that:
- Tolerance develops within 24 hours of a single dose (observable in mouse HTR model)
- Progressive tolerance develops over 4 days of repeated administration
- Tolerance is 5-HT₂AR-dependent and independent of β-arrestin-2
- Cross-tolerance between psychedelics (DOI ↔ LSD) but not between psychedelic and non-psychedelic 5-HT₂AR agonists

By class extrapolation, 4-HO-DET tolerance begins almost immediately after ingestion and resets over approximately 7 days — consistent with the database brief's values (half-life 3 days, full reset 7 days), which are supported by class evidence for all classical psychedelics.

### Cross-Tolerance

Cross-tolerance is expected with all 5-HT₂A agonist psychedelics: LSD, psilocybin/psilocin, mescaline, DMT, other 4-HO and 4-AcO tryptamines (de la Fuente Revenga et al. 2022 [Ref 10]; Buckholtz et al. 1990 [Ref 11]).

### Dependence Liability

No physical dependence or withdrawal syndrome has been documented for 4-HO-DET or for classical psychedelics as a class. The database brief's characterization as "not habit-forming" is supported by class evidence: classical psychedelics do not activate the mesolimbic dopamine system in a manner associated with addiction; rapid tolerance development itself limits compulsive use patterns (Nichols 2018 [Ref 12]).

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## Interactions

### Tramadol — **DANGEROUS**

Tramadol is a synthetic opioid that inhibits the serotonin transporter (SERT) in human SERT-transfected HEK293 cells (Baldo 2018 [Ref 25]). Combined with a 5-HT₂A agonist, tramadol may increase synaptic serotonin concentrations, creating risk of **serotonin syndrome** — a potentially life-threatening condition characterized by hyperthermia, agitation, neuromuscular hyperactivity, and autonomic instability. The FDA issued a Drug Safety Communication in 2016 linking the entire class of opioid analgesics to serotonin toxicity risk, specifically noting tramadol (Baldo 2018 [Ref 25]; Park et al. 2014 [Ref 30]).

**⚠️ FLAG FOR REVIEW:** The "dangerous" classification for tramadol in the database brief is mechanistically supported by tramadol's SERT inhibition (Baldo 2018 [Ref 25]). However, no published case report of a tramadol + 4-HO-DET interaction specifically was identified. The classification is inferred from pharmacological mechanism and class evidence.

### Cannabis — **Unknown**

No published data on 4-HO-DET + cannabis interaction. The drug-drug interaction systematic review (Halman et al. 2024 [Ref 33]) found some LSD + cannabis data but no tryptamine-specific cannabis interaction data. The interaction is genuinely unknown and the "unknown" classification in the database brief is appropriate.

### Monoamine Oxidase Inhibitors (MAOIs)

By class pharmacology, MAOIs (irreversible or reversible) are expected to potentiate 4-HO-DET effects via inhibition of MAO-A-mediated tryptamine degradation and by increasing synaptic serotonin. Risk of serotonin syndrome. This interaction is not specifically documented for 4-HO-DET but is a class-level warning based on MAOI + tryptamine pharmacology.

### SSRIs and SNRIs

Based on LSD and psilocybin interaction data (Halman et al. 2024 [Ref 33]): SSRIs may attenuate or blunt psychedelic effects via 5-HT₂A receptor downregulation from chronic serotonin elevation. Simultaneous use carries theoretical serotonin syndrome risk, though clinical psychedelic studies have not found serious adverse events from this combination in controlled settings. Interaction classification requires editorial determination.

### Lithium

Combination of lithium with psychedelics has case reports of increased seizure risk and erratic behavior. This is a known dangerous combination for classical psychedelics as a class (not specific to 4-HO-DET but relevant).

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## Legal Status

### United States
4-HO-DET is **not federally scheduled** under the Controlled Substances Act as of 2026. However, as a compound that is pharmacologically and structurally analogous to psilocin (Schedule I), it may be subject to prosecution under the **Federal Analogue Act (FAA, 21 U.S.C. § 813)** if intended for human consumption. No formal DEA scheduling action was identified for 4-HO-DET specifically. [Ref 22, web-retrieved]

### United Kingdom
4-HO-DET is controlled as a **Class A** substance under the **Misuse of Drugs Act 1971** via the generic tryptamine catch-all clause, which was incorporated in 1977 to capture N,N-dialkyl substituted tryptamines with hallucinogenic activity. Additionally, the **Psychoactive Substances Act 2016** blanket-prohibits production, supply, import, and export of all psychoactive substances not otherwise whitelisted. 4-HO-DET is covered by both provisions. [Ref 22, web-retrieved]

### Canada
4-HO-DET is **not explicitly controlled** under the Canadian Controlled Drugs and Substances Act as of 2025. [web-retrieved]

### Germany
4-HO-DET is likely controlled under the **Neue-psychoaktive-Stoffe-Gesetz (NpSG)**, Germany's new psychoactive substances law, which covers structural classes of tryptamines with psychoactive properties. However, specific verification of 4-HO-DET's NpSG status was not confirmed in the peer-reviewed literature. [web-retrieved]

### Australia
4-HO-DET's specific scheduling under the Australian Standard for the Uniform Scheduling of Medicines and Poisons (SUSMP) was not confirmed in this research. It is likely classified as a **Schedule 9 Prohibited Substance** by extension of the broad tryptamine provisions, but this was not directly verified. [web-retrieved]

**⚠️ FLAG FOR REVIEW:** Legal status for Germany and Australia is inferred from class-based NPS legislation and not confirmed by direct government source. Canada "not controlled" status is from web-retrieved community source, not a primary legal database. These should be verified against current scheduling databases before publication.

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## Clinical Trials

A search of ClinicalTrials.gov for "4-HO-DET", "diethyltryptamine", and related terms returned **zero results**. No registered clinical trials for 4-HO-DET were identified in any jurisdiction as of April 2026. The compound's clinical use was confined to the European psycholytic therapy era of the 1960s (Leuner and Baer), which predates modern trial registration requirements.

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## Community Feedback Analysis

**No community feedback was submitted** in Part A2 of the brief for this substance. Standard research directives applied.

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## Gaps & Flags

### Safety-Critical Data Requiring Human Review

1. **⚠️ SMILES string unverified:** PubChem CID 9991554 confirmed, but the API did not return a SMILES string. Structurally derived SMILES (CCN(CC)CCc1c[nH]c2cccc(O)c12) should not be published without API verification. Generation agent should request SMILES directly from PubChem CID 9991554 canonical SMILES field.

2. **⚠️ No substance-specific Ki/EC₅₀ binding values:** No published binding affinity data for 4-HO-DET at any receptor was found. All receptor pharmacology is inferred from: (a) structural analogy to psilocin; (b) Gatch 2021's DOM discrimination (qualitative); (c) Glatfelter 2023's binding screen which included the diethyl variant but for which compound-specific values were not accessible. Generation agent must label all binding affinity claims as class-inferred, not substance-specific.

3. **⚠️ Duration discrepancy — dose/duration data requires editorial judgment:**
   - TIHKAL #16 [Ref 20]: duration = **4–6 hours**
   - Database brief and PsychonautWiki: duration = **5–7 hours**
   - The 1-hour discrepancy at each end may reflect dose-dependence (higher community doses → longer duration) or variant salt forms. TIHKAL's Leuner clinical data specifically praised "shorter duration." No published study resolves this. Editor should determine which range to present and at what dose reference point.

4. **⚠️ Dose range discrepancy at upper end:**
   - TIHKAL [Ref 20]: 10–25 mg oral (all documented doses)
   - Database brief: Threshold 5 mg, Light 10–15 mg, Common 20–30 mg, **Strong 30–45 mg, Heavy 45+ mg**
   - The "strong" (30–45 mg) and "heavy" (45+ mg) categories exceed Shulgin's published experience range. These higher-dose classifications are not validated by any published source. The "common" upper bound of 30 mg slightly exceeds Shulgin's maximum of 25 mg. All dose tiers above 25 mg should be treated as community-reported with no primary-source validation.

5. **⚠️ No published pharmacokinetic data for 4-HO-DET:** All PK inferred from psilocin (4-HO-DMT) and DMT analogy. Half-life, bioavailability, Tmax, and metabolic pathway are unconfirmed for 4-HO-DET specifically.

6. **⚠️ No published toxicological data:** No LD₅₀, NOAEL, or organ toxicity data for 4-HO-DET in any species. Toxic dose genuinely unknown.

7. **⚠️ No published case reports of adverse events:** The adverse effect profile is entirely based on TIHKAL bioassay reports (N=handful of experiences) and Leuner's unpublished 1960s clinical observations referenced in TIHKAL. No peer-reviewed case reports of 4-HO-DET-associated adverse events were found.

8. **⚠️ Legal status — Germany and Australia unconfirmed:** Inferred from generic NPS/tryptamine legislation; not verified from primary government sources.

9. **⚠️ Tramadol interaction — "dangerous" classification is mechanistically supported but not documented for this specific compound:** The classification is sound based on tramadol's SERT inhibition (Baldo 2018 [Ref 25]), but no published case report exists for tramadol + 4-HO-DET specifically. The classification should be retained with appropriate sourcing.

10. **No clinical trials identified:** The substance has no registered clinical trials in ClinicalTrials.gov as of April 2026.

### Data Gaps (Not Safety-Critical)

- **Repke et al. (1970s–1980s) publications on 4-hydroxytryptamines** are referenced historically [Ref 22] but were not identified via PubMed search, likely because they may be in non-indexed journals or predated electronic indexing. The generation agent should acknowledge Repke's research historically without citing specific papers.
- **Leuner and Baer's clinical publications** were conducted in German-language journals in the 1960s and are not indexed in PubMed. Their work is referenced via TIHKAL [Ref 20] and Passie et al. 2022 [Ref 16] but primary German-language sources were not verified.
- **Stereochemistry:** 4-HO-DET does not have chiral centers (unlike some conformationally constrained analogs studied by Gerasimov et al. 1999 [Ref 28]). No stereoisomer data is relevant.
- **Physical properties beyond MP:** logP, water solubility, and pKa were not found in accessible literature. Storage instability in air (phenol oxidation) is documented [Ref 20].