Diphenhydramine Side Effects

Some side effects of diphenhydramine may not be reported. Always consult your doctor or healthcare specialist for medical advice. You may also report side effects to the FDA.

For the Consumer

Applies to diphenhydramine: oral capsule, oral disintegrating strip, oral liquid, oral tablet, oral tablet chewable, oral tablet disintegrating

Get emergency medical help if you have any of these signs of an allergic reaction while taking diphenhydramine: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Stop using diphenhydramine and call your doctor at once if you have:

• fast or uneven heart rate;

• mood changes;

• tremor, seizure (convulsions);

• easy bruising or bleeding, unusual weakness;

• shortness of breath; or

• little or no urinating.

Common side effects may include:

• dizziness, drowsiness;

• dry mouth, nose, or throat;

• constipation;

• blurred vision; or

• feeling nervous or restless.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects.

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

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 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.

Hypersensitivity

Hypersensitivity side effects have included rash, pruritus and eczema. Photosensitivity reactions have also been reported.

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.

Gastrointestinal

Gastrointestinal side effects have been usually mild and included nausea and dry mouth.

Cardiovascular

Cardiovascular side effects have included hypotension, tachycardia, and palpitations.

Ocular

Ocular side effects have included blurred vision, diplopia, and dry eyes due to anticholinergic effects.

Genitourinary

Genitourinary side effects have included urinary retention and dysuria as a result of the anticholinergic effects of diphenhydramine.

Hematologic

Hematologic side effects such as hemolytic anemia, thrombocytopenia, and agranulocytosis have been rarely caused by antihistamines.

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