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Medical Uses: – Diphenhydramine is a first-generation antihistamine used to treat allergies, itchiness, common cold, insomnia, motion sickness, and extrapyramidal symptoms. – It has local […]

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Medical Uses:
– Diphenhydramine is a first-generation antihistamine used to treat allergies, itchiness, common cold, insomnia, motion sickness, and extrapyramidal symptoms.
– It has local anesthetic properties and is used for acute allergic reactions in emergency departments.
– Available in topical formulations for itching relief.

Special Populations and Contraindications:
– Not recommended for people over 60 and children under six; second-generation antihistamines are preferred.
– Excreted in breast milk and may cause paradoxical reactions, especially in children.
– Contraindications include premature infants, neonates, breastfeeding individuals, and those on monoamine oxidase inhibitors.

Overdose and Interactions:
– Commonly misused OTC drug in the U.S., with symptoms of extreme overdose including abdominal pain, coma, and death.
– Overdose may lead to seizures, hallucinations, and severe dizziness, requiring symptomatic and supportive care.
– Interactions with alcohol, CNS depressants, and monoamine oxidase inhibitors intensify effects.

Pharmacokinetics and Chemistry:
– Oral bioavailability ranges from 40% to 60%, metabolized by cytochrome P450 enzymes.
– Chemical structure discovered in 1943, first prescription antihistamine approved by the FDA in 1946.
– Diphenhydramine is a diphenylmethane derivative with analogues like orphenadrine, nefopam, and tofenacin.

Recreational Use and Names:
– Diphenhydramine is used recreationally for calming effects, mild euphoria, and hallucinations.
– Known as Benadryl in the U.S., Canada, and South Africa, with other trade names like Dimedrol and Nytol.
– Over-the-counter formulations like ZzzQuil and Sominex contain diphenhydramine for sleep aid purposes.

Diphenhydramine (Wikipedia)

Diphenhydramine (DPH) is an antihistamine and sedative mainly used to treat allergies, insomnia, and symptoms of the common cold. It is also less commonly used for tremors in parkinsonism, and nausea. It is taken by mouth, injected into a vein, injected into a muscle, or applied to the skin. Maximal effect is typically around two hours after a dose, and effects can last for up to seven hours.

Clinical data
Trade namesBenadryl, Unisom, Nytol, others
License data
  • AU: A
Routes of
By mouth, intramuscular, intravenous, topical, rectal
Drug classfirst-generation antihistamine (ethanolamine), anticholinergic, hallucinogen (deliriant)
ATC code
Legal status
Legal status
Pharmacokinetic data
Protein binding98–99%
MetabolismLiver (CYP2D6, others)
Elimination half-lifeRange: 2.4–13.5 h
ExcretionUrine: 94%
Feces: 6%
  • 2-(diphenylmethoxy)-N,N-dimethylethanamine
CAS Number
PubChem CID
CompTox Dashboard (EPA)
ECHA InfoCard100.000.360 Edit this at Wikidata
Chemical and physical data
Molar mass255.361 g·mol−1
3D model (JSmol)
  • O(CCN(C)C)C(c1ccccc1)c2ccccc2
  • InChI=1S/C17H21NO/c1-18(2)13-14-19-17(15-9-5-3-6-10-15)16-11-7-4-8-12-16/h3-12,17H,13-14H2,1-2H3 checkY
 ☒NcheckY (what is this?)  (verify)

Common side effects include sleepiness, poor coordination and an upset stomach. Its use is not recommended in young children or the elderly. There is no clear risk of harm when used during pregnancy; however, use during breastfeeding is not recommended. It is a first-generation H1-antihistamine and it works by blocking certain effects of histamine, which produces its antihistamine and sedative effects. Diphenhydramine is also a potent anticholinergic, which means it also works as a deliriant at much higher than recommended doses as a result. Its sedative and deliriant effects have led to some cases of recreational use.

Diphenhydramine was first developed by George Rieveschl and came into commercial use in 1946. It is available as a generic medication. It is sold under the brand name Benadryl, among others. In 2021, it was the 242nd most commonly prescribed medication in the United States, with more than 1 million prescriptions.

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