Diphenhydramine
Diphenhydramine is a first-generation antihistamine that blocks the H1 histamine receptor to relieve allergic reactions, hay fever, hives, and itching. Because the molecule readily crosses the blood-brain barrier, it also produces pronounced drowsiness, which is why it doubles as a short-term sleep aid, and its antiemetic action helps with motion sickness and nausea. A small molecule (C17H21NO), it carries anticholinergic activity that causes dry mouth, urinary retention, and similar effects, and its half-life of about 2 to 8 hours limits each dose's duration. These central and anticholinergic properties make it less suitable for regular long-term use than newer, non-sedating antihistamines. Diphenhydramine is an approved medicine sold widely over the counter for allergy and sleep indications.
A first-generation antihistamine widely used for allergic reactions, hay fever, hives, itching, and as a short-term sleep aid. It also has antiemetic properties used for motion sickness and nausea. Because it crosses the blood-brain barrier, it causes significant drowsiness and has anticholinergic side effects such as dry mouth and urinary retention, making it unsuitable for regular, long-term use.
Peso molecular
255,3550 g/mol
LogP
3,30
TPSA
12,50 Ų
Regla de cinco de Lipinski
Cumple
Áreas terapéuticas
Clases de fármacos
Mecanismo de acción
First-generation H1 antihistamine with anticholinergic properties.
Pharmacokinetics (PK)
Pharmacodynamics (PD)
First-generation H1 antihistamine with anticholinergic properties.
Estructura 2D
Cite this structure
Embed this structure
SMILES
CN(C)CCOC(c1ccccc1)c1ccccc1
InChI
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
Molecular Formula
C17H21NO
HBD / HBA
- / 2
Enlaces Rotables
6
Átomos Pesados
19
Diphenhydramine, a sedating antihistamine, substantially increases CNS and respiratory depression when combined with opioids like oxycodone.
Diphenhydramine potentiates morphine-induced CNS and respiratory depression and may increase the risk of fatal overdose.
Diphenhydramine's potent anticholinergic effect directly opposes donepezil's pro-cholinergic mechanism, negating therapeutic benefit and increasing risk of delirium in elderly patients.
Diphenhydramine may modestly reduce aspirin absorption and slightly impair its antiplatelet efficacy through delayed gastric emptying; the clinical significance is generally low.
Diphenhydramine adds to the sedative effects of alprazolam, increasing the risk of excessive CNS depression, falls, and cognitive impairment.
Diazepam and diphenhydramine produce additive CNS depression, with risk of profound sedation, cognitive impairment, and falls.
No side effects recorded
Side effect data is not yet available for this drug.
Preguntas frecuentes
A first-generation antihistamine widely used for allergic reactions, hay fever, hives, itching, and as a short-term sleep aid. It also has antiemetic properties used for motion sickness and nausea. Because it crosses the blood-brain barrier, it causes significant drowsiness and has anticholinergic side effects such as dry mouth and urinary retention, making it unsuitable for regular, long-term use.
First-generation H1 antihistamine with anticholinergic properties.
Key pharmacokinetic parameters for Diphenhydramine: Half-life: 2-8 hours.
Yes, Diphenhydramine is an approved drug. It has reached clinical phase 4. It is classified as a Small molecule.
Related Drugs
Same Drug Class
References & Data Sources
- ChEMBL — European Bioinformatics Institute (EBI). CHEMBL657. Open-access bioactivity database.
- PubChem — National Center for Biotechnology Information (NCBI). CID 3100. Chemical information database.
Data aggregated from publicly available pharmacological databases. Last updated 2026-03-04.
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