Note: This document contains side effect information about diphenhydramine. Some dosage forms listed on this page may not apply to the brand name Benadryl.

Applies to diphenhydramine: oral capsules and tablets, parenteral injection.

Side effects include:

Sedation, sleepiness, dizziness, disturbed coordination, epigastric distress, thickening of bronchial secretions.

For Healthcare Professionals

Applies to diphenhydramine: compounding powder, injectable solution, oral capsule, oral disintegrating strip, oral liquid, oral tablet, oral tablet chewable, oral tablet disintegrating.

General

The most commonly reported side effects included somnolence, dizziness, and incoordination.^[Ref]

Nervous system

Common (1% to 10%): Sedation/somnolence/sleepiness, drowsiness, unsteadiness, dizziness, headache, attention disturbance

Rare (0.01% to 0.1%): Extrapyramidal effects, tremor, convulsions

Frequency not reported: Paresthesia, dyskinesia/muscle dyskinesia, vertigo, neuritis, incoordination, psychomotor impairment, activation of epileptogenic foci^[Ref]

Drowsiness usually diminishes after a few days.^[Ref]

Gastrointestinal

Common (1% to 10%): Dry mouth

Frequency not reported: Gastrointestinal disturbance, nausea, vomiting, constipation, diarrhea, dyspepsia, epigastric distress^[Ref]

Other

Common (1% to 10%): Fatigue

Frequency not reported: Lassitude, tinnitus, acute labyrinthitis, asthenia, chills, impaired performance (including impaired driving, work, and/or information processing)^[Ref]

Psychiatric

Rare (0.01% to 0.1%): Confusion, depression, sleep disturbances

Frequency not reported: Paradoxical excitation/excitation, agitation, increased energy, restlessness, nervousness, euphoria, anxiety, hallucinations, insomnia, irritability^[Ref]

Cardiovascular

Rare (0.01% to 0.1%): Palpitations, hypotension, arrhythmia

Frequency not reported: Tachycardia, chest tightness, extrasystoles^[Ref]

Hematologic

Rare (0.01% to 0.1%): Blood disorders

Frequency not reported: Hemolytic anemia, thrombocytopenia, agranulocytosis^[Ref]

Hypersensitivity

Rare (0.01% to 0.1%): Hypersensitivity reactions

Frequency not reported: Angioedema, anaphylactic shock^[Ref]

Hepatic

Rare (0.01% to 0.1%): Liver dysfunction^[Ref]

Dermatologic

Frequency not reported: Rash, urticaria, skin rashes, erythema, photosensitivity, pruritus, drug rash, excessive perspiration^[Ref]

Respiratory

Frequency not reported: Dyspnea, thickening of bronchial secretions, throat tightening, wheezing, nasal stuffiness, dry nose or throat^[Ref]

Genitourinary

Frequency not reported: Urinary hesitancy/difficulty/retention, dysuria, early menses^[Ref]

Ocular

Frequency not reported: Blurred vision, dry eyes, diplopia^[Ref]

Metabolic

Frequency not reported: Increased appetite, anorexia^[Ref]

Musculoskeletal

Frequency not reported: Muscle twitching/weakness^[Ref]