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What the label lists and what reports show

Diphenhydramine side effects

Diphenhydramine's FDA label lists its adverse reactions in its own words. FAERS holds 164,832 reports naming it through July 30, 2026; the reaction reported most often, leaving out the conditions it is used for, product-use terms and outcomes, is fatigue (15,900 reports).

  • Generic listed

Check it at the source: the diphenhydramine FDA label on DailyMed (effective November 18, 2025, Heritage Pharmaceuticals Inc. d/b/a Avet Pharmaceuticals Inc.); the FDA FAERS public dashboard.

What does the label list?

From the label: adverse reactions

The most frequent adverse reactions are italicized. General Urticaria; drug rash; anaphylactic shock; photosensitivity; excessive perspiration; chills; dryness of mouth, nose and throat. Cardiovascular System Hypotension, headache, palpitations, tachycardia, extrasystoles. Hematologic System Hemolytic anemia, thrombocytopenia, agranulocytosis. Nervous System Sedation, sleepiness, dizziness, disturbed coordination, fatigue, confusion, restlessness, excitation, nervousness, tremor, irritability, insomnia, euphoria, paresthesia, blurred vision, diplopia, vertigo, tinnitus, acute labyrinthitis, neuritis, convulsions. Gastrointestinal System Epigastric distress, anorexia, nausea, vomiting, diarrhea, constipation. Genitourinary System Urinary frequency, difficult urination, urinary retention, early menses. …

Source: FDA drug label, Heritage Pharmaceuticals Inc. d/b/a Avet Pharmaceuticals Inc., effective November 18, 2025 (SPL set 6178d3a1-0741-49a4-be81-c4f7d29f8b2a), via openFDA; the full label on DailyMed

What do FAERS reports show?

164,832 reports list diphenhydramine among the medicines taken, each a report of something that happened, not proof the medicine caused it; 22,785 are coded as a death and 47,567 as a hospital stay. Counts follow how widely a medicine is used and watched, and they are not a measure of how risky it is. Of the 21 reactions below, 8 are named by the same term (in US spelling) in the label's adverse reactions, warnings or patient leaflet; a reaction the label does not name may still be there under another word, and a report does not show that the medicine caused it.

Reports received each year

The 25 most reported reactions

  • Off Label Use (a use or a product term, not a reaction)17,967
  • Fatigue (named in the label)15,900
  • Nausea (named in the label)14,216
  • Headache (named in the label)13,710
  • Pain (a use or a product term, not a reaction)11,686
  • Drug Ineffective (a use or a product term, not a reaction)11,415
  • Dyspnoea10,850
  • Pruritus10,347
  • Infusion Related Reaction9,943
  • Arthralgia9,146
  • Rash (named in the label)9,109
  • Diarrhoea (named in the label)8,782
  • Pyrexia8,349
  • Vomiting (named in the label)7,912
  • Dizziness (named in the label)7,597
  • Malaise7,560
  • Cough7,503
  • Pneumonia7,471
  • Urticaria (named in the label)7,276
  • Blood Pressure Increased7,165
  • Weight Decreased6,755
  • Nasopharyngitis6,514
  • Sinusitis6,247
  • Asthenia6,056
  • Death (an outcome recorded in the report)6,028

Source: FDA Adverse Event Reporting System (FAERS) via openFDA, reports through July 30, 2026; reactions as MedDRA preferred terms

What next?

Diphenhydramine: the full record
label, generics, price, shortages, recalls
Side effects hub
the most reported medicines and reactions