Genahist Side Effects
Generic Name: diphenhydramine
Note: This page contains information about the side effects of diphenhydramine. Some of the dosage forms included on this document may not apply to the brand name Genahist.
More frequent side effects include: sedation and thickening of bronchial secretions. See below for a comprehensive list of adverse effects.
For the Consumer
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
Nervous system side effects have been reported frequently. These have included depression with drowsiness and sedation in nearly all patients treated. Motor skills may be impaired. Dystonic reactions have been reported after single doses of diphenhydramine (the active ingredient contained in Genahist) [Ref]
The CNS depressant effect of diphenhydramine parallels its plasma concentrations. The plasma concentration threshold for sedation is 30 to 42 ng/mL, and to cause mental impairment is 58 to 74 ng/mL. Patients should be warned against driving while taking diphenhydramine.
Dystonic reactions have been accompanied by dizziness, mental confusion, rigidity, lip and tongue protrusion, trismus, torticollis, and swallowing difficulties and generally resolve spontaneously. Toxic encephalopathy has been reported in a child with chicken pox treated generously with topical diphenhydramine.
Delirium has been reported in elderly patients with mild dementia following a small oral dose of diphenhydramine.[Ref]
Hypersensitivity side effects have included rash, pruritus and eczema. Photosensitivity reactions have also been reported.[Ref]
Most commonly, hypersensitivity has manifested itself in patients receiving systemic drug after being sensitized to it by topical application. Sensitization with systemic administration has also been reported.[Ref]
Gastrointestinal side effects have been usually mild and included nausea and dry mouth.[Ref]
Cardiovascular side effects have included hypotension, tachycardia, and palpitations.[Ref]
Ocular side effects have included blurred vision, diplopia, and dry eyes due to anticholinergic effects.[Ref]
Genitourinary side effects have included urinary retention and dysuria as a result of the anticholinergic effects of diphenhydramine (the active ingredient contained in Genahist) [Ref]
Hematologic side effects such as hemolytic anemia, thrombocytopenia, and agranulocytosis have been rarely caused by antihistamines.[Ref]
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Not all side effects for Genahist may be reported. You should always consult a doctor or healthcare professional for medical advice. Side effects can be reported to the FDA here.
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