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Benadryl: Full Drug Profile

Medically reviewed by Min Clinic Staff | Updated: January 2026

Benadryl - General Information

A histamine H1 antagonist used as an antiemetic, antitussive, for dermatoses and pruritus, for hypersensitivity reactions, as a hypnotic, an antiparkinson, and as an ingredient in common cold preparations. It has some undesired antimuscarinic and sedative effects.

 

Pharmacology of Benadryl

Benadryl is an antihistamine of the ethanolamine class. Ethanolamine antihistamines have significant antimuscarinic activity and produce marked sedation in most patients. In addition to the usual allergic symptoms, the drug also treats irritant cough and nausea, vomiting, and vertigo associated with motion sickness. It also is used commonly to treat drug-induced extrapyramidal symptoms as well as to treat mild cases of Parkinson's disease. Rather than preventing the release of histamine, as do cromolyn and nedocromil, diphenhydramine competes with free histamine for binding at HA-receptor sites. Benadryl competitively antagonizes the effects of histamine on HA-receptors in the GI tract, uterus, large blood vessels, and bronchial muscle. Ethanolamine derivatives have greater anticholinergic activity than do other antihistamines, which probably accounts for the antidyskinetic action of diphenhydramine. This anticholinergic action appears to be due to a central antimuscarinic effect, which also may be responsible for its antiemetic effects, although the exact mechanism is unknown.

 

Benadryl for patients

Patients taking diphenhydramine hydrochloride should be advised that this drug may cause drowsiness and has an additive effect with alcohol.

Patients should be warned about engaging in activities requiring mental alertness such as driving a car or operating appliances, machinery, etc.

 

Benadryl Interactions

Diphenhydramine hydrochloride has additive effects with alcohol and other CNS depressants (hypnotics, sedatives, tranquilizers, etc).

MAO inhibitors prolong and intensify the anticholinergic (drying) effects of antihistamines.

 

Benadryl Contraindications

Use in Newborn or Premature Infants: This drug should not be used in newborn or premature infants.

Use in Nursing Mothers: Because of the higher risk of antihistamines for infants generally, and for newborns and prematures in particular, antihistamine therapy is contraindicated in nursing mothers.

Antihistamines are also contraindicated in the following conditions: Hypersensitivity to diphenhydramine hydrochloride and other antihistamines of similar chemical structure.

Injection

Use as a Local Anesthetic: Because of the risk of local necrosis, this drug in the parenteral from should not be used as a local anesthetic.

 

Additional information about Benadryl

Benadryl Indication

For the treatment of symptoms associated with Vertigo/Meniere's disease, nausea and vomiting, motion sickness and insect bite.

Mechanism Of Action
Benadryl competes with free histamine for binding at HA-receptor sites. This antagonizes the effects of histamine on HA-receptors, leading to a reduction of the negative symptoms brought on by histamine HA-receptor binding.
Drug Interactions
Atomoxetine The CYP2D6 inhibitor could increases the effect and toxicity of atomoxetine
Food Interactions
Avoid alcohol.
Generic Name
Diphenhydramine
Synonyms
Diphenhydramine Base; Diphenhydramine Hcl; Diphenhydramine Salicylate; Diphenylhydramine
Drug Category
Histamine H1 Antagonists; Anti-Allergic Agents; Hypnotics and Sedatives; Antitussives; Antipruritics; Antiparkinson Agents; Antidyskinetics; Antiemetics; Anesthetics; Ethanolamine Derivatives
Drug Type
Small Molecule; Approved
Other Brand Names containing Diphenhydramine
Aleryl; Alledryl; Aller-Med; Allerdryl; Allergan B; Allergeval; Allergical; Allergin; Allergina; Allergival; Allermax Caplets; Ambodryl; Amidryl; Antistominum; Antitussive; Antomin; Automin; Bagodryl; Banophen; Banophen Caplets; Baramine; Beldin; Belix; Ben-Allergin; Bena; Benachlor; Benadrin; Benadryl; Benadryl Allergy; Benadryl Preservative Free; Benapon; Benodin; Benodine; Benylan; Benylin; Benzantine; Benzhydramine; Benzhydraminum; Benzhydril; Benzhydroamina; Benzhydryl; Betramin; Compoz; Dabylen; Debendrin; Dermistina; Dermodrin; Desentol; Diabenyl; Diabylen; Dibendrin; Dibenil; Dibondrin; Difedryl; Difenhydramin; Difenidramina; Dihidral; Dimedrol; Dimedryl; Diphantine; Diphen; Diphen Cough; Diphenhist; Diphenhist Captabs; Dormarex 2; Dryistan; Drylistan; Dylamon; Etanautine; Genahist; Histaxin; Hyadrine; Hydramine; Hyrexin; Ibiodral; Medidryl; Mephadryl; Nausen; Nervine Nighttime Sleep-Aid; Novamina; Nytol Quickcaps; Nytol Quickgels; Probedryl; Restamin; Rigidil; Rigidyl; Siladryl; Silphen; Sleep-Eze D; Sleep-Eze D Extra Strength; Sominex; Soverin; Syntedril; Syntodril; Torinal; Twilite Caplets; Unisom Sleepgels Maximum Strength; Vena; Vicks Formula 44;
Absorption
Quickly absorbed with maximum activity occurring in approximately one hour.
Toxicity (Overdose)
LD50=500 mg/kg (orally in rats). Considerable overdosage can lead to myocardial infarction (heart attack), serious ventricular dysrhythmias, coma and death.
Protein Binding
98 to 99%
Biotransformation
Hepatic and renal
Half Life
1-4 hours
Dosage Forms of Benadryl
Liquid Intravenous
Chemical IUPAC Name
2-[di(phenyl)methoxy]-N,N-dimethylethanamine
Chemical Formula
C17H21NO
Organisms Affected
Humans and other mammals