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WARNINGDELIRIANTS CAUSE DANGEROUS PSYCHOSIS & ARE EXTREMELY TOXIC
Hallucinations under the influence of deliriants are experienced as genuine reality, blending seamlessly with the external environment. This is in combination with overwhelmingly uncomfortable physical side effects and a complete absence of recreational or therapeutic value.
Diphenhydramine
2-(Diphenylmethoxy)-N,N-dimethylethanamine
DPH, Benadryl, Nytol, Sominex, Unisom SleepMelts
Diphenhydramine is a first-generation antihistamine of the ethanolamine class1, first developed in 1943 by George Rieveschl2 and widely available over the counter under the brand name Benadryl1. Primarily used to treat allergies and insomnia1, it possesses anticholinergic properties2 functionally similar to tropane alkaloids found in nightshade plants. At high doses, it acts as a potent deliriant, producing intensely realistic hallucinations alongside significant physical discomfort and dysphoria.
Dosage & Duration
Dosage
Doses are population estimates that vary widely between individuals.
Threshold~25 mg
Light25-150 mg
Moderate150-300 mg
Strong300-500 mg
Heavy500+ mg
Bioavailability
40-60%
The dose-response relationship for diphenhydramine is nonlinear. At amounts under 300 mg, effects generally include restlessness, muscle relaxation, and altered bodily sensations. Above 500 mg, a deliriant state may emerge, characterized by vivid visual and auditory hallucinations. Doses between these ranges often produce dysphoria and significant discomfort. Amounts approaching or exceeding 2 grams carry serious risk of fatal overdose, especially in combination with stimulants or MAOIs.
Duration
Onset30-90 minutes
Come Up45-90 minutes
Peak1-4 hours
Offset2-6 hours
After Effects2-24 hours
Total3-10 hours
Half-life
2.4-9.3 hours
Subjective Effects
Legacy content. A statistically backed ontology from Mindstate Design Labs is coming soon.
Effects vary widely by individual, dose, and context.
Physical
The physical effects of DPH are usually described as extremely uncomfortable. They can be broken down into several components which progressively intensify proportional to dosage. These are described below and generally include:
The levels of dysphoria experienced, however, vary between people with a very small percentage of users reporting that they do not seem to experience them at all.
Cognitive
The head space of DPH is described by many as generally negative and dysphoric throughout the trip, often consisting of extreme paranoia and feelings of impending doom. It is largely confusing and disorienting often leading to a complete inability to communicate or understand normal language. The most prominent of these effects include:
Visual
Distortions
As for visual distortions and alterations, effects experienced are detailed below:
Hallucinatory States
The effects of DPH are extremely efficient at inducing delirious hallucinations which can be broken into the two categories described below:
Suppressions
DPH does not enhance visual stimuli in the way that psychedelics do. Instead, they tend to degrade and decrease visual aptitude resulting in increasing hallucinations and degrading vision. These components are detailed below.
Auditory
The auditory effects of DPH are common in their occurrence and exhibit a range of effects which commonly includes:
See also: Subjective Effects of Deliriants
Pharmacology
Pharmacodynamics
Diphenhydramine acts primarily as an inverse agonist of the histamine H1 receptor, both peripherally (where it reduces allergic symptoms) and within the central nervous system (where it produces sedation and drowsiness).3 It is also a potent competitive antagonist at muscarinic acetylcholine receptors, and this anticholinergic activity is considered primarily responsible for its deliriant properties at high doses.citation needed Additional pharmacological actions include inhibition of serotonin reuptake, blockade of intracellular sodium channels and voltage-gated potassium channels, weak antagonism at the 5-HT2C receptor, and inhibition of histamine N-methyltransferase.
Pharmacokinetics
Diphenhydramine has an oral bioavailability of approximately 40 to 60%, reflecting extensive first-pass metabolism in the liver, with peak plasma concentrations occurring about 2 to 3 hours after administration.citation needed It is metabolized primarily through two successive N-demethylations catalyzed by the cytochrome P450 enzymes CYP2D6 (which shows the highest affinity for the substrate), CYP1A2, CYP2C9, and CYP2C19. The resulting metabolites undergo further acetylation or oxidation, followed by conjugation with glycine and glutamine before excretion in urine. Only about 1% of a dose is excreted unchanged. The elimination half-life in healthy adults ranges from approximately 2.4 to 9.3 hours.
Dangerous
Highest riskThese combinations are considered extremely harmful and should always be avoided. Reactions to these drugs taken in combination are highly unpredictable and have a potential to cause death.
Unsafe
AvoidThere is considerable risk of physical harm when taking these combinations, they should be avoided where possible.
Caution
Use cautionThese combinations are not usually physically harmful, but may produce undesirable effects, such as physical discomfort or overstimulation. Extreme use may cause physical health issues. Synergistic effects may be unpredictable. Care should be taken when choosing to use this combination.
Tolerance
Tolerance timelines are rules of thumb, not exact schedules, and vary widely between individuals and use patterns.
Full Tolerance
Tolerance to the effects of diphenhydramine develops rapidly with repeated use, requiring increasingly larger doses to achieve the same intensity of effects. Full tolerance can develop within a few consecutive uses.
Cross Tolerance
Deliriants
Baseline Reset
Tolerance returns to baseline after approximately 1-2 weeks of abstinence. Some sources suggest that full-effect experiences can only occur every 2-4 weeks.
Harm Potential
Addiction & Dependence
Psychological
LowGenerally considered to have low abuse potential due to its dysphoric effects; most individuals who try recreational doses do not wish to repeat the experience. However, cases of abuse and addiction have been documented, particularly among adolescents without access to other drugs and individuals with mental health conditions such as schizophrenia who may self-administer large doses to treat extrapyramidal symptoms.citation needed
Physical
LowProduces dependence with chronic use, though the severity and specific withdrawal symptoms are not well-documented in the literature.citation needed
Toxicity
Cardiovascular
High doses and overdoses can cause cardiotoxicity including arrhythmias, severe tachycardia, QT prolongation, and cardiovascular collapse; myocardial infarction and serious ventricular dysrhythmias have been reported with considerable overdosage.citation needed
Urinary System
Regular recreational use has been anecdotally linked to kidney and bladder damage with symptoms similar to ketamine cystitis; these reports are associated with chronic high-dose use patterns and remain unstudied.
Central Nervous System
Chronic high-dose use may cause persisting hallucinations and impairments in cognition and memory; cumulative anticholinergic use later in life has been tentatively linked to increased risk of cognitive decline and dementia.citation needed
Hepatic
The drug is extensively metabolized by the liver; caution is advised in individuals with hepatic impairment as half-life is prolonged in patients with chronic liver disease.citation needed
Musculoskeletal
Large overdoses may cause rhabdomyolysis, particularly when excessive physical activity occurs during intoxicated states where the user cannot distinguish reality from hallucinations.citation needed
Psychosis Risk
Causes psychosis and delirium at significantly higher rates than other hallucinogens such as psychedelics and dissociatives. Toxic psychosis, delirium, and complete inability to distinguish hallucinations from reality are characteristic features at recreational doses. Users may lose control of their actions and respond to delusional environments, risking injury to themselves or others. Numerous experience reports describe psychotic delirium, amnesia, and serious consequences including hospitalization and death.
Seizure Risk
High doses and overdoses have been linked to seizures and convulsions, with risk increasing particularly at overdose-level doses.4 Children are more susceptible to CNS excitation including convulsions at elevated doses.5 Benzodiazepines are recommended as first-line treatment to decrease seizure likelihood in overdose cases.citation needed
History & Culture
Discovery and Development
Diphenhydramine was discovered in 1943 by chemist George Rieveschl and his student Fred Huber during research into muscle relaxants at the University of Cincinnati.citation needed Huber performed the initial synthesis, after which Rieveschl partnered with pharmaceutical company Parke-Davis to…
Trip Reports
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Legality
International
Diphenhydramine is not scheduled under the 1961, 1971, or 1988 United Nations drug-control conventions. UNODC's Legislative and Policy System lists diphenhydramine hydrochloride among substances not under international control.
By Country
Controlled / restricted1
ZambiaControlled substanceIllegal to possess and sell. The Zambian Drug Enforcement Commission actively enforces restrictions, and foreign nationals have been detained and charged with drug trafficking offenses for possessing over-the-counter medications containing diphenhydramine, even in small quantities.59 Passports may be confiscated and imprisonment is possible.
Prescription1
United KingdomOver-the-counter (age-restricted)Available without prescription at pharmacies and retail outlets. Typically not sold to individuals under 16 years of age, though enforcement varies by retailer.55
Legal / decriminalized16
United StatesLegal (regulated)Widely available over-the-counter as an FDA-approved medication.58 Legal to purchase, possess, and consume without a prescription or license. Sales for human consumption are regulated by the FDA, with each formulation requiring specific approval.
BrazilLegal (regulated)Brazil’s Lista de Medicamentos Isentos de Prescrição lists two cloridrato de difenidramina combinations: lozenges containing 5 mg with ammonium chloride and sodium citrate, and an oral solution containing 2.5 mg/mL with the same substances. Products matching the listed active ingredients, dosage forms, concentrations, and indications are exempt from prescription under the LMIP.
DenmarkLegal (regulated)Danish Medicines Agency notice on sedating antihistamines28
The Danish Medicines Agency states that Benylan, which contains diphenhydramine, changed to the HA18 dispensing classification. It is available only from pharmacies to people aged 18 or older.
FranceLegal (regulated)ANSM public medicines database record for ACTIFED RHUME JOUR ET NUIT29
Diphenhydramine hydrochloride is an active substance in the authorised ACTIFED RHUME JOUR ET NUIT medicine. ANSM classifies this combination product in Liste I and as prescription-only. This classification does not necessarily apply to every diphenhydramine formulation.
IndonesiaLegal (regulated)BPOM product-registration record EREG10010512600060: VALDRES, registration number DTL0721633517A133
BPOM lists VALDRES as an Obat (drug) containing diphenhydramine hydrochloride, with registration number DTL0721633517A1. The record was issued on 1 July 2026 and is valid until 1 July 2031.
JapanLegal (regulated)Japan’s Pharmaceuticals and Medical Devices Agency classifies diphenhydramine hydrochloride injection as a prescription medicine for use on the prescription of a physician or other qualified prescriber. PMDA also lists a diphenhydramine hydrochloride tablet as a non-prescription medicine, so supply classification is product-specific.
SingaporeLegal (regulated)Poisons Act 193846
Diphenhydramine and its salts are listed in the Poisons List to the Poisons Act 1938. The Act treats listed substances as poisons and requires a licence for importation, possession for sale, sale, or offering for sale; retail sale is generally restricted to licensed premises under a pharmacist’s personal supervision.
South KoreaLegal (regulated)MFDS Drug Safety Korea product record for 그밤엔연질캡슐(디펜히드라민염산염)49
The Ministry of Food and Drug Safety lists 그밤엔연질캡슐(디펜히드라민염산염) as a non-prescription medicine (일반의약품) containing diphenhydramine hydrochloride 50 mg per capsule.
SpainLegal (regulated)Soñodor difenhidramina 50 mg comprimidos is an authorised Spanish medicine containing diphenhydramine hydrochloride. The AEMPS CIMA record classifies it as Sin receta and commercially available without a prescription.
SwitzerlandLegal (regulated)Diphenhydramine hydrochloride is the active substance in Benocten®, a medicinal product listed by Swissmedic. Swissmedic patient information states that Benocten® may be obtained from a pharmacy without a medical prescription.
Not scheduled3
BelgiumNot scheduledThe Belgian AFMPS/FAGG Nustasium 50 mg marketing authorisation BE180485 and patient leaflet (latest approval December 2024) identify the product; the controlled-substance framework is established by the Royal Decree of 6 September 2017. The current Justel text and AFMPS consolidated Annexes I-V set out the relevant controlled-substance schedules.141516171819202122
The official leaflet expressly states Délivrance libre, and the SmPC confirms diphenhydramine hydrochloride in Nustasium 50 mg (BE180485). The current Justel decree and AFMPS schedule materials do not identify diphenhydramine as a controlled narcotic or psychotropic, and no applicable Annex IV generic family covers it. The AFMPS warns that only Belgian Official Gazette annexes have formal legal force, while its consolidated PDFs are reference versions. The dispensing conditions for other diphenhydramine formulations or foreign products may differ.
BulgariaOver-the-counterAvailable without prescription. Sold under brand names including Calmaben and combination products such as APAP Night.25
PolandNot scheduledThe consolidated schedule and July 2026 amendment contain no diphenhydramine/difenhydramine entry. The official register identifies Luminastil 50 mg diphenhydramine hydrochloride tablets with OTC packages; its leaflet is expressly for adults and says not to use it below 18, which is a product-specific indication and use warning. Pharmaceutical Law Article 71a's under-18 refusal rule is limited to OTC products containing substances on the Article 71a(5) list, which contains pseudoephedrine, codeine, and dextromethorphan, not diphenhydramine. Article 71a does not impose a blanket statutory 18+ sales restriction on diphenhydramine.
References
Source Pages
Citations
- Diphenhydramine. LiverTox: Clinical and Research Information on Drug-Induced Liver Injury (2017). https://www.ncbi.nlm.nih.gov/books/NBK548470/123
- Diphenhydramine: A Review of Its Clinical Applications and Potential Adverse Effect Profile. Journal of Pediatric Pharmacology and Therapeutics (2025). https://pmc.ncbi.nlm.nih.gov/articles/PMC12288571/12
- StatPearls. StatPearls (2021). https://www.ncbi.nlm.nih.gov/books/NBK526010/1
- Diphenhydramine Toxicity. (2021). https://pubmed.ncbi.nlm.nih.gov/32491510/1
- Diphenhydramine- diphenhydramine hydrochloride injection, solution. DailyMed (n.d.). https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=921b9f64-1096-46db-866a-67f0f9ff6790#diphenhydramine-injection-label1
- FDA warns about serious problems with high doses of the allergy medicine diphenhydramine (Benadryl). U.S. Food & Drug Administration (2020-09-24). https://www.fda.gov/drugs/drug-safety-and-availability/fda-warns-about-serious-problems-high-doses-allergy-medicine-diphenhydramine-benadryl1
- Healthdirect Australia medicine record, Diphenhydramine. healthdirect.gov.au (n.d.). https://www.healthdirect.gov.au/medicines/medicinal-product/aht%2C22404/diphenhydramine1
- Healthdirect Australia medicine record, Diphenhydramine. healthdirect.gov.au (n.d.). https://www.healthdirect.gov.au/medicines/brand/amt%2C732691000168100/benadryl-original1
- Benadryl Original. healthdirect (n.d.). https://www.healthdirect.gov.au/medicines/brand/amt,732691000168100/benadryl-original1
Further Reading
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Josie Kins · Updated the article · also 1,4-Butanediol, 1B-LSD, 1cP-AL-LAD and 573 more
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