by Nicole Evans M.D.

Created on: November 06, 2010

Diphenhydramine, better known as Benadryl, is a medication that is available over-the-counter.  There are a large number of uses for Diphenhydramine, from relief of common cold and allergy symptoms, to short-term treatment of insomnia, to the management of severe anaphylactic allergic reactions.

Despite the fact that Diphenhydramine is available in every corner drug store, the use of this medication does require certain precautions.  Diphenhydramine has numerous side effects that potential consumers should be aware of.    

Diphenhydramine is a first generation antihistamine and is more sedating than the later generation antihistamines such as cetirizine (Zyrtec) and loratadine (Claritin).  However, as a first generation antihistamine it is also more useful in treating sleep problems, itchy skin, nausea and vomiting and even mild anxiety.

More unusual uses of Diphenhydramine include it’s use in the early treatment of tremor in Parkinson’s disease.  Diphenhydramine is also used to relieve acute allergic reactions after a patient receives plasma or blood transfusion.

Diphenhydramine side effects:

The most common side effects of Diphenhydramine include sedation, sleepiness, dizziness, difficulty performing coordinated movements, epigastric distress (stomach ache), and thickening of mucus secretions from the respiratory tract.

Diphenhydramine can also cause side effects such as headache, urinary retention, dry mouth, dizziness, confusion, low blood pressure and heart rhythm irregularities.

In children, there is also the risk of diminished mental alertness, as well as risk of a paradoxical reaction that may cause excitation in young kids.

Diphenhydramine toxicity in children:

Importantly there is a risk of diphenhydramine toxicity when doubling up on the Diphenhydramine dose in children by giving it by mouth and using a concomitant topical preparation that contains Diphenhydramine.  The symptoms of Diphenhydramine toxicity include:

-dilated pupils

-flushed face

-hallucinations

-ataxic gait

-urinary retention.

Disease-relatied contraindications to Diphenhydramine:

There are certain medical conditions that require a patient to consult their doctor before self-treating with over-the-counter Diphenhydramine preparations.  These conditions include glaucoma, emphysema, chronic bronchitis, or difficulty urinating due to prostatic hypertrophy.

Specifically, Diphenhydramine should be used with caution in people with increased intraocular pressure, angle-closure glaucoma, peptic ulcer, obstruction at the neck of the bladder, symptomatic prostatic enlargement, active bronchial asthma or a history of lower respiratory disease, hyperthyroidism, and/or cardiovascular disease such as hypertension.

Diphenhydramine is widely available and commonly used.  However, this medication has many side effects, including potential dangerous events in young children and in people with certain medical conditions.  Individuals should always speak with their physician for any questions

Source: Lexi-Comp Online. Accessed Mar 26, 2010.

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