Diphenhydramine

# Research Output: Diphenhydramine

## Chemical Identity

**PubChem CID:** 3100 (api_verified, [Ref 1])
**Molecular Formula:** C₁₇H₂₁NO [Ref 1]
**Molecular Weight:** 255.35 g/mol [Ref 1]
**InChIKey:** ZZVUWRFHKOJYTH-UHFFFAOYSA-N [Ref 1]
**IUPAC Name:** 2-benzhydryloxy-N,N-dimethylethanamine [Ref 1]
**SMILES:** CN(C)CCOC(c1ccccc1)c1ccccc1 (derived from IUPAC; not returned by PubChem API directly — SMILES not in brief seed data and not API-confirmed from this run; note for generation agent)
**CAS Number:** 58-73-1 (free base); 147-24-0 (HCl salt) — sourced from standard chemical databases; not API-confirmed in this run; flag for verification
**Systematic class:** Ethanolamine antihistamine (first-generation)
**Stereochemistry:** Diphenhydramine has one chiral center at the benzhydryl ether carbon and is sold as a **racemate** (racemic mixture of R and S enantiomers). No stereoselective commercial preparation is standard. Published literature does not extensively address differential activity of individual enantiomers for DPH specifically [Ref 2]; enantiomeric potency data gap noted.
**Salt forms used clinically:** Diphenhydramine hydrochloride (most common OTC formulation); diphenhydramine citrate; dimenhydrinate (diphenhydramine 8-chlorotheophyllinate, used for motion sickness)

**Notes on seed data:**
- Seed data listed SMILES, molecular formula, molecular weight, InChIKey, and PubChem CID as blank. PubChem CID 3100 is confirmed. Formula (C₁₇H₂₁NO) and MW (255.35) confirmed. InChIKey confirmed.
- Seed data chemical class listed "Phenethylamine, Ethanolamine" — the Phenethylamine classification requires a flag. DPH is an **ethanolamine antihistamine** structurally; it does not share the classical phenethylamine scaffold. The diphenylmethoxy group differentiates it. This may be a database classification error. **⚠️ FLAG for editorial review.**
- Seed data pharmacological class listed "Serotonin reuptake inhibitor" — DPH has documented weak serotonin reuptake inhibition (confirmed by published pharmacology literature [Ref 41]), but this is a minor action far from the primary mechanism. H1 antagonism and muscarinic antagonism are primary. Listing SRI as a primary class overstates this activity.

---

## Pharmacology

### Mechanism of Action

Diphenhydramine is a **first-generation H1 receptor inverse agonist** that crosses the blood-brain barrier readily due to its lipophilicity (log P ~3.3). Unlike second-generation antihistamines, it distributes extensively into the CNS, causing sedation as a defining property [Ref 2, Ref 41].

#### Histamine H1 Receptor
The primary pharmacological target. DPH acts as an **inverse agonist** at the H1 receptor, reducing constitutive receptor activity rather than merely blocking agonist binding [Ref 2, Ref 41]. Binding affinity at H1 in human astrocytoma cell membranes (via [³H]mepyramine displacement): **Ki ≈ 5 nM** (0.005 µM) [Ref 3, Ref 4]. This high H1 affinity accounts for its potent antihistaminic, antipruritic, and antiallergic effects. The H1 receptor crystal structure (co-crystallized with doxepin at 3.1 Å, PDB: 3RZE) reveals a large orthosteric binding pocket occupied by the bulky diphenylmethoxy moiety of ethanolamine-class antihistamines like DPH [Ref 2].

#### Muscarinic Acetylcholine Receptors
DPH is a **competitive antagonist at muscarinic receptors (M1–M5)**, with sub-micromolar affinity for cardiac muscarinic receptors (Liu et al. 2006 [Ref 5] report apparent sub-micromolar Ki by Langendorff preparation). The IUPHAR histamine receptor review (Panula et al. 2015 [Ref 2]) and a comprehensive metabolic review (Sharma & Hamelin 2003 [Ref 6]) confirm DPH's significant antimuscarinic profile. This accounts for anticholinergic symptoms: dry mouth, urinary retention, tachycardia, constipation, blurred vision, and at high doses, delirium and hallucinations.

#### Sodium Channels (Voltage-Gated)
DPH is an **intracellular sodium channel blocker**, producing local anesthetic properties comparable in mechanism to lidocaine [Ref 41]. In overdose, sodium channel blockade is responsible for QRS prolongation, wide-complex tachycardia, and ventricular dysrhythmias [Ref 17, Ref 13]. Carroll et al. (2026 [Ref 17]) note that DPH "binds preferentially to open sodium channels and dissociates slowly," similar to tricyclic antidepressants. This explains why sodium bicarbonate reverses cardiac conduction abnormalities [Ref 19].

#### hERG (Kv11.1) Potassium Channels
DPH blocks cardiac hERG channels, causing **QT interval prolongation** and risk of torsade de pointes at toxic concentrations [Ref 42]. The StatPearls toxicity chapter (NBK557578 [Ref 42]) documents "prolongation of the QT interval and a flattening of the T-wave" via potassium channel blockade. This is confirmed by the review of sodium bicarbonate for QRS/QT management [Ref 19] and lipid emulsion case reports [Ref 18].

#### NMDA Receptors
Föhr et al. (2015 [Ref 35]) demonstrated that DPH acts as an **open channel blocker of NMDA (N-methyl-D-aspartate) glutamate receptors**. This is a novel mechanism supporting DPH's sedative and analgesic properties beyond H1 and muscarinic antagonism. NMDA receptor antagonism may also contribute to the dissociative character of delirium at high doses.

#### Histamine N-Methyltransferase (HNMT) Inhibition
Horton et al. (2005 [Ref 2, context]) showed DPH inhibits HNMT with Ki in the 10–100 nM range by occupying the histamine-binding site of this metabolic enzyme. This action may extend the duration of histamine signaling and has implications for understanding DPH's pharmacological breadth.

#### Serotonin Reuptake
DPH has documented weak serotonin transporter (SERT) inhibition [Ref 41]. This is a minor pharmacological action — the SERT affinity is considerably lower than its H1 affinity. Its clinical relevance is uncertain. Published literature on SERT inhibition by DPH lacks specific Ki/IC50 values in the reviewed sources. **⚠️ FLAG: No primary source with a specific SERT Ki value was located in this research run. The "Serotonin reuptake inhibitor" pharmacological class label in the seed data may overstate this activity.**

### Pharmacokinetics

Human pharmacokinetic data are available from multiple controlled studies [Ref 7, Ref 8, Ref 9, Ref 10, Ref 11, Ref 41]:

| Parameter | Value | Source |
|-----------|-------|--------|
| Oral bioavailability | 72% (±8%) | StatPearls [Ref 41] |
| Oral bioavailability (older review) | 40–60% | Paton & Webster 1985 [Ref 7] |
| Tmax (oral) | 1.5–2.5 hours | [Ref 8, Ref 10, Ref 41] |
| Cmax (50mg oral) | 47.8–61 ng/ml | [Ref 9, Ref 10] |
| Half-life (healthy adults) | ~9 hours | StatPearls [Ref 41] |
| Half-life (alternative estimate) | 4–6 hours | Gielsdorf et al. 1986 [Ref 10], Paton 1985 [Ref 7] |
| Half-life (liver disease) | 9–15 hours | Paton & Webster 1985 [Ref 7] |
| Half-life (children) | ~5.4 hours | StatPearls [Ref 41] |
| Volume of distribution | 17 L/kg | StatPearls [Ref 41] |
| Volume of distribution (older) | >4 L/kg | Paton & Webster 1985 [Ref 7] |
| Plasma protein binding | ~98% | StatPearls [Ref 41] |
| Clearance | 5–12 ml/min/kg | Paton & Webster 1985 [Ref 7] |
| Unchanged renal excretion | <2% | StatPearls [Ref 41] |

**⚠️ DISCREPANCY NOTE:** Oral bioavailability ranges differ between the 1985 review (40–60%) and StatPearls (72%). This may reflect differences in formulation, analytical methods (RIA vs. GLC), or updated pharmacokinetic modelling. The StatPearls figure of 72% is more recent and cites more specific methodology. The generation agent should note both values and the uncertainty.

**Metabolism:** DPH undergoes substantial first-pass hepatic metabolism, primarily via **CYP2D6** (N-demethylation to mono- and dinordiphenhydramine) and flavin-containing monooxygenases (N-oxide formation) [Ref 6, Ref 41]. Glucuronidation of the alicyclic amine produces N-glucuronides (~7%) [Ref 6]. Less than 2% is excreted unchanged in urine [Ref 41].

**CYP2D6 Inhibition:** DPH is a clinically significant **inhibitor of CYP2D6**, elevating plasma concentrations of co-administered CYP2D6 substrates such as metoprolol and propranolol [Ref 6, Ref 34]. This is documented as a clinically significant drug-drug interaction [Ref 6].

**Blood-Brain Barrier Penetration:** DPH readily crosses the BBB due to high lipophilicity, accounting for its CNS sedative and deliriant effects. This property distinguishes it from second-generation antihistamines (e.g., loratadine, fexofenadine) [Ref 2].

---

## History

**Discovery (1943):** Diphenhydramine was synthesized by chemist **George Rieveschl** and his student Fred Huber at the **University of Cincinnati** in 1943 while investigating compounds related to muscle relaxants and synthetic alternatives to scopolamine [Ref 31, Ref 40]. The discovery was thus not a targeted antihistamine program but an incidental finding during a broader pharmacological investigation.

**Industrial Development:** Rieveschl partnered with **Parke-Davis** (later acquired by Pfizer), which licensed the patent and conducted clinical development. Parke-Davis marketed diphenhydramine under the trade name **Benadryl** [Ref 31].

**FDA Approval (1946):** Diphenhydramine became the **first prescription antihistamine approved by the FDA in the United States** in 1946. This was a landmark event in allergy pharmacotherapy [Ref 31, Ref 40].

**Patent (1947):** Rieveschl was granted the patent in 1947 [Ref 30].

**Over-the-Counter Transition (1982/1985):** Diphenhydramine was approved for OTC sale in the United States — 1982 for some formulations, 1985 for others [Ref 30, Ref 32]. This dramatically expanded its accessibility and subsequent misuse potential.

**Antiemetic Discovery:** The antiemetic (anti-nausea/motion sickness) properties of dimenhydrinate (DPH 8-chlorotheophyllinate) were discovered serendipitously when a patient being treated with DPH for urticaria reported improvement in motion sickness — a classic example of pharmacological repurposing [Ref 40]. This history of H1 antagonist development is described in peer-reviewed literature by Sanger & Andrews (2018 [Ref 40]).

**Contemporary Regulatory Trend (2026):** Several countries have moved to restrict DPH availability due to increasing misuse and serious adverse events. Australia reclassified DPH to **Schedule 4 (prescription-only)** effective **July 1, 2026**, driven in part by rising emergency department presentations related to DPH misuse [Ref 53]. Germany, Netherlands, and Sweden have also implemented prescription-only requirements.

---

## Subjective Effects

### Therapeutic Dose Range (25–100 mg)

Controlled human studies document the following at therapeutic doses:

- **Sedation:** Significant, dose-dependent [Ref 36, Ref 37]. Turner et al. (2006 [Ref 36]) showed statistically significant subjective sedation in all doses tested (50–100 mg) compared to placebo in 12 healthy volunteers. Temazepam 30 mg was more sedating than DPH 75 mg [Ref 37].
- **Reduced sleep latency:** Confirmed in RCTs [Ref 36].
- **Psychomotor impairment:** Impaired digit symbol substitution test (DSST), choice reaction time, and sustained attention at 50–100 mg [Ref 36]. Psychomotor impairment at 75 mg was less than temazepam 30 mg but similar to temazepam 15 mg [Ref 37].
- **Memory impairment:** DPH 100 mg impaired prompted recall at 2 hours post-dose, comparable to lorazepam 1.5 mg [Ref 36].
- **Anticholinergic symptoms:** Dry mouth, tachycardia, urinary hesitancy, blurred vision (mild at therapeutic doses).
- **Interaction potentiation:** DPH 100 mg significantly enhances the CNS depressant effects of diazepam and alcohol, worsening psychomotor performance and subjective feelings [Ref 39].

**Note on elderly subjects:** Lines et al. (1997 [Ref 38]) found no drowsiness or cognitive impairment in elderly volunteers receiving DPH 50 mg × 10 doses over 4 days, contrasting with expected findings. This suggests the elderly may be **less** CNS-sensitive than younger adults — contrary to common clinical assumption. **⚠️ FLAG for editorial note in article.**

### Supratherapeutic/Deliriant Range (200–700+ mg)

At doses substantially above therapeutic range, DPH produces an **anticholinergic deliriant** syndrome. Published case reports and toxicological surveillance data document:

- **Hallucinations (visual, auditory, tactile):** Confirmed in 46.5% of pediatric DPH-only exposures in a large surveillance dataset (n=2028) [Ref 33]. Case report of 27-year-old with optical and acoustic hallucinations, clouded consciousness [Ref 23]. Community reports describe characteristic "shadow people" hallucinations (Psychonaut community; no controlled published study specifically documenting this).
- **Delirium:** Severe thought disorganization, confusion, disorientation [Ref 23, Ref 42, Ref 41].
- **Agitation:** Confirmed in 33.9% of pediatric exposures [Ref 33].
- **Tachycardia:** Confirmed in 53.4% of pediatric exposures [Ref 33].
- **Mydriasis:** Confirmed in 26.3% of pediatric exposures [Ref 33].
- **Restlessness and akathisia-like movements:** Consistent with anticholinergic toxidrome.
- **Somnolence:** Confirmed in 34.7% [Ref 33].

The subjective experience of deliriant DPH is widely documented in community harm-reduction forums (Erowid, Reddit), and consistently described as profoundly dysphoric with vivid hallucinations indistinguishable from reality, "shadow people," tactile hallucinations, and severe cognitive disorganization. **No published controlled studies of recreational/deliriant DPH exist for ethical reasons.** Community reports converge on a generally unpleasant, fear-inducing experience — highly dysphoric compared to classical psychedelics.

**Effect taxonomy mapping from seed data (consistent with evidence):**
- Perception: External hallucinations, internal hallucinations, auditory hallucinations, shadow people, touch hallucination/suppression, visual haze — all consistent with anticholinergic delirium [Ref 23, Ref 33]
- Thinking: Delirium, delusions, confusion, thought disorganization — confirmed [Ref 23, Ref 41]
- Body: Dry mouth, tachycardia, pupil constriction (listed in seed) — **⚠️ DISCREPANCY: Anticholinergic drugs cause MYDRIASIS (pupil dilation), not pupil constriction. Seed data listing "Pupil constriction" appears incorrect. Confirmed mydriasis 26.3% in pediatric data [Ref 33]. FLAG for correction.**
- Self: Derealization — plausible, consistent with anticholinergic delirium but no specific published source found

---

## Safety & Toxicity

### Animal LD50 Data (from MSDS sources [Ref 47])
- Rat, oral: **500 mg/kg**
- Mouse, oral: **164 mg/kg**
- Rat, intraperitoneal: 82 mg/kg
- Rat, subcutaneous: 201 mg/kg

### Human Toxicity Thresholds (from forensic/clinical literature)

| Level | Dose | Blood Concentration |
|-------|------|---------------------|
| Therapeutic | 25–100 mg | 50–100 ng/ml |
| Toxic | ~300 mg | >1,000 ng/ml (estimated) |
| Severe | 1,000 mg (1 g+) | Variable |
| Fatal (typical range) | >2,000 mg | 3,300–285,000 ng/ml |

- The StatPearls toxicity chapter states moderate symptoms at ~300 mg and severe symptoms at ≥1,000 mg [Ref 42].
- Forensic blood DPH concentrations in fatal cases ranged from 3,300 to 228,000 ng/ml in the Cook County study (n=25) [Ref 12] and 14,640–285,000 ng/ml in the literature review [Ref 12].
- Eckes et al. (2013 [Ref 15]) used 5 µg/ml (5,000 ng/ml) as a cutoff between toxic and lethal concentrations, though they note individual case interpretation is required.
- Karch (1998 [Ref 16]) reported blood DPH levels of 5,000–35,000 ng/ml in 4 autopsy cases.
- The seed data note "fatal at amounts close to or exceeding 2 grams" — **confirmed as a reasonable threshold** consistent with published forensic data [Ref 12, Ref 15, Ref 16].

### Cardiac Mechanisms in Overdose

1. **Sodium channel blockade:** QRS widening, wide-complex tachycardia, ventricular fibrillation [Ref 17, Ref 21, Ref 13, Ref 19]. DPH binds preferentially to open sodium channels with slow dissociation [Ref 17].
2. **hERG potassium channel blockade:** QT prolongation, risk of torsade de pointes [Ref 42].
3. **Treatment:** Sodium bicarbonate (first-line for sodium channel blockade), lidocaine (adjunct for refractory VT [Ref 17]), IV lipid emulsion (for hemodynamic instability [Ref 18]), VA-ECMO (for cardiac arrest [Ref 14]).
4. **Hemodialysis:** Not effective due to DPH's high lipophilicity and large Vd [Ref 42].

### Anticholinergic Toxidrome

Classic presentations include: hot/dry/red/mad (hyperthermia, dry skin, flushing, delirium), tachycardia, mydriasis, urinary retention, ileus. Physostigmine (acetylcholinesterase inhibitor) can reverse the syndrome [Ref 45, Ref 46]; associated with fewer intubations when used vs. non-antidote therapy [Ref 45].

### Epidemiology
- **Pediatric exposures (2008–2015):** 2,028 DPH-only adverse events identified; 5 deaths (0.2%), mostly homicidal [Ref 33].
- **Cook County Forensic (2015–2024):** 25 DPH-only fatalities; 20/25 certified as suicides [Ref 12]; majority had history of depression.
- **TikTok "Benadryl Challenge" (2023 case report):** 14-year-old fatality with postmortem DPH 49,658 ng/ml [Ref 34].
- **Recreational/intentional misuse:** Documented as a common pattern in clinical toxicology series [Ref 24].

### Chronic Toxicity
- **Anticholinergic burden:** Cumulative anticholinergic exposure (to which DPH chronically contributes a high burden) is associated with increased risk of incident dementia in large epidemiological studies [Ref 44, Ref 39]. This is a major public health concern, particularly for elderly users.
- **AASM guideline:** The American Academy of Sleep Medicine (2017 [Ref 50]) recommends **against** the use of diphenhydramine for chronic insomnia treatment, given tolerance, adverse effect profile, and lack of rigorous efficacy data.

### Respiratory Depression
Seed data lists "Respiratory depression" as an effect. **Confirmed at toxic doses** — several fatal case reports involve respiratory failure [Ref 42]. At therapeutic doses, respiratory depression is not clinically significant in healthy adults, though caution is warranted in patients with COPD, sleep apnea, or concurrent CNS depressants.

---

## Harm Reduction

### Contraindications (from published clinical literature)
- **Neonates and premature infants:** Contraindicated (risk of fatal respiratory depression) [Ref 41]
- **Breastfeeding:** Contraindicated (excreted in breast milk, sedation in infants) [Ref 41]
- **Narrow-angle glaucoma:** Contraindicated due to mydriatic/cycloplegic effects [Ref 41]
- **Benign prostatic hyperplasia:** Risk of acute urinary retention [Ref 41]
- **Hepatic impairment:** Prolonged half-life (up to 15h) increases risk of accumulation [Ref 7]
- **Elderly patients:** High anticholinergic burden, falls risk, cognitive effects; listed in Beers Criteria as potentially inappropriate medication [general geriatric pharmacology consensus; specific Beers search not performed in this run — **⚠️ FLAG**]
- **Children under 2:** FDA recommends against antihistamine/decongestant products in children < 2 years [Ref 39]
- **Restless Legs Syndrome:** Antihistamines including DPH can **worsen** RLS [Ref 52] — important contraindication for patients using DPH as a sleep aid who have underlying RLS.

### Drug Interactions (Evidence-Based)
1. **Alcohol:** Potentiates psychomotor impairment and CNS depression (double-blind controlled study [Ref 39])
2. **Benzodiazepines:** Additive CNS depression confirmed experimentally [Ref 39]
3. **Other CNS depressants (opioids, sedatives, antipsychotics):** Additive CNS and respiratory depression — class-level evidence [Ref 41]
4. **CYP2D6 substrates (metoprolol, propranolol, antidepressants):** DPH inhibits CYP2D6, raising blood levels — clinically significant DDI with metoprolol [Ref 6]
5. **Other anticholinergic drugs:** Additive anticholinergic burden; cumulative effects on cognition, urinary function, cardiac conduction [Ref 41]
6. **MAOIs:** Listed as interaction concern in clinical references due to additive CNS effects; specific published evidence in controlled studies not identified in this research run — **⚠️ FLAG**

### Testing and Identification
No specific reagent test strip data identified for recreational DPH context. DPH can be detected in standard clinical immunoassay toxicology screens and confirmed by GC-MS or LC-MS/MS [Ref 34].

### Emergency Response
- Suspected overdose: Call poison control/emergency services immediately
- Activated charcoal if within 1 hour of ingestion and airway is protected [Ref 42]
- Sodium bicarbonate for QRS widening [Ref 19]
- Benzodiazepines for seizures [Ref 42]
- Physostigmine for severe anticholinergic delirium (if no contraindications) [Ref 45, Ref 46]
- 4-hour observation minimum after oral exposure [Ref 42]

---

## Tolerance & Dependence

### Tolerance
- Rapid tolerance (tachyphylaxis) to sedative effects with repeated use is well-documented [Ref 50, Ref 7]
- Antihistaminic effects also show tolerance with repeated dosing
- Cross-tolerance within the deliriant class (as stated in seed data) is biologically plausible via shared anticholinergic/H1 mechanisms but specific published cross-tolerance studies were not identified in this run
- **Seed data:** "Full reset: 1.5 weeks" — this figure is not confirmed by published primary literature identified in this research run. **⚠️ FLAG: No published primary source for the 1.5-week tolerance reset timeline identified. Likely derived from community reports.**

### Dependence
- A systematic review and case report (Erbe & Bschor 2013 [Ref 43]) documents DPH addiction and describes detoxification protocols. DPH produces physical and psychological dependence with chronic use.
- Seed data: "Formation: produces dependence with chronic use" — **confirmed** [Ref 43].
- Withdrawal features: insomnia rebound, anxiety, irritability — consistent with chronic antihistamine use cessation; specific withdrawal severity scale data not published.

---

## Interactions

### CYP2D6-Mediated Drug Interactions
DPH is metabolized by and inhibits CYP2D6 [Ref 6]. Clinically significant interactions:
- **Metoprolol:** Elevated plasma concentrations; increased risk of bradycardia/hypotension [Ref 6]
- **Propranolol:** Similar mechanism [Ref 6]
- **Other CYP2D6 substrates** (codeine, tramadol, many antidepressants): potential for elevated levels or reduced prodrug activation (codeine → morphine impaired)

### Pharmacodynamic Interactions
- **CNS depressants (alcohol, benzodiazepines, opioids, sedative-hypnotics):** Additive/synergistic CNS and respiratory depression — highest clinical priority interaction [Ref 39]
- **Anticholinergics (TCAs, antipsychotics, antispasmodics, other H1 antihistamines):** Additive anticholinergic toxidrome risk [Ref 40]
- **MAOIs:** Potential additive CNS/anticholinergic effects — no controlled clinical study identified; **⚠️ FLAG for editorial verification**

### Sodium Bicarbonate Interaction (Treatment Context)
Sodium bicarbonate reverses DPH-induced sodium channel blockade [Ref 19] — relevant for emergency management rather than co-administration risk.

---

## Legal Status

| Jurisdiction | Status | Notes |
|--------------|--------|-------|
| United States | OTC (unscheduled) | Prescription 1946; OTC 1982 (some formulations), 1985 (additional); not a controlled substance |
| United Kingdom | OTC | Available without prescription |
| Canada | OTC | Available without prescription |
| Australia | **Schedule 4 (prescription-only)** | Effective **July 1, 2026**; reclassified by TGA due to rising ED presentations and misuse [Ref 53] |
| Germany | Prescription-only | Not OTC |
| Netherlands | Prescription-only | Not OTC |
| Sweden | Prescription-only | Not OTC |
| EU generally | Variable | Several member states have restricted OTC access |

**Note:** This is a rapidly evolving regulatory area. The Australia rescheduling (July 2026) is a significant recent development. Other jurisdictions may follow. DPH is **not a scheduled controlled substance** in any reviewed jurisdiction (it is not subject to DEA scheduling in the US).

---

## Clinical Trials

**NCT02578186** — "Evaluation of Diphenhydramine Hydrochloride Effects in Subjects With Occasional Sleeplessness"
- **Status:** COMPLETED
- **Phase:** Phase 4
- **Sponsor:** Procter and Gamble
- **Condition:** Occasional Sleeplessness
- **Relevance:** Direct investigation of DPH efficacy and safety for OTC sleep indication

**NCT03688464** — "Treatment of Nighttime Pruritus in Atopic Dermatitis"
- **Status:** WITHDRAWN
- **Phase:** Early Phase 1
- **Sponsor:** University of Nebraska
- **Condition:** Atopic Dermatitis

**DPH as Active Placebo:** DPH (50 mg) was used as an active placebo in the psilocybin for alcohol use disorder RCT (Bogenschutz/Ross 2022 [Ref 48]), confirming its mild sedative effect is distinguishable from a true psychedelic response but produces enough subjective effect to serve as placebo comparator.

**Note:** No published trials specifically investigating DPH as a deliriant or investigating its recreational/psychoactive use were identified (ethical reasons). No active trials for DPH were identified in ClinicalTrials.gov as of April 2026.

---

## Community Feedback Analysis

No community feedback was submitted in Part A2 of the brief.

---

## Gaps & Flags

### 🚨 Safety-Critical Flags

1. **Pupil constriction listed as effect in seed data — LIKELY INCORRECT.** Anticholinergic drugs cause MYDRIASIS (pupil dilation), not constriction. Pediatric surveillance data confirms mydriasis in 26.3% of cases [Ref 33]. The seed data "Pupil constriction" effect may be a database error. **High priority for correction.**

2. **Bioavailability discrepancy:** StatPearls (72%) vs older review (40–60%). Generation agent should acknowledge uncertainty. Both values should be presented with their sources.

3. **Half-life discrepancy:** Older studies (4–6h) vs StatPearls (9h). The longer value is more consistent with the Vd of 17 L/kg and renal excretion pattern. The shorter values may reflect formulation or analytical differences.

4. **MAOI interaction:** Listed as a concern in clinical references but no specific controlled study data identified. Cannot verify severity.

5. **Beers Criteria specific citation:** Not retrieved in this research run. Beers Criteria inclusion is widely mentioned in clinical practice for DPH but a specific published Beers Criteria document was not fetched.

### ⚠️ Data Not Verified Against Primary Sources

6. **Tolerance reset at 1.5 weeks:** Seed data claim not confirmed by any published source. Likely from community reports only.

7. **Cross-tolerance to deliriant class:** Biologically plausible but specific published cross-tolerance studies not identified.

8. **SMILES string:** Not returned by PubChem API; derived from IUPAC name. Should be confirmed against published structure.

9. **CAS number (58-73-1):** Not API-confirmed in this run; standard chemical database value but not independently verified.

10. **SERT Ki value:** DPH serotonin reuptake inhibition is documented but no specific Ki/IC50 value at SERT was found in published primary literature reviewed. "Serotonin reuptake inhibitor" as a primary pharmacological class label is likely overstated.

### ℹ️ Data Absent from Published Literature

11. **Controlled studies of recreational/deliriant DPH experience:** None exist for obvious ethical reasons. Effect descriptions at high doses come exclusively from case reports of poisoning and community reports.

12. **Stereoselective pharmacology:** No published data on differential activity of R vs S enantiomers of DPH specifically.

13. **Erowid/community "shadow people" hallucinations:** Well-known community-reported phenomenon, but no peer-reviewed primary study specifically documenting this as a named effect of DPH.

14. **Pediatric pharmacokinetics (comprehensive):** The StatPearls half-life in children (5.4h) is noted, but comprehensive pediatric PK studies were not retrieved.

15. **Sigma receptor binding:** PDSP/NIMH screening data for DPH at sigma receptors was not located in the reviewed literature; no specific Ki value found.

16. **Pregnancy category/teratogenicity:** No specific published study retrieved in this run. DPH is generally considered Category B (US historical classification); this should be verified.