The most frequent adverse reactions are underscored.
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
GI System: Epigastric distress, anorexia, nausea, vomiting, diarrhea, constipation
GU System: Urinary frequency, difficult urination, urinary retention, early menses
Respiratory System: Thickening of bronchial secretions, tightness of chest or throat and wheezing, nasal stuffiness
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.