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What is this medication?

Antihistamine, First Generation

Allergies, insomnia, prevention or treatment of motion sickness, antitussive, management of drug-induced extrapyramidal symptoms, parkinsonian syndrome.

Brand Name US: Allergy Relief, Banophen, Diphenist, Genahist, Geri-Dryl, Naramin, Ormir, zzzQuil
Brand Name Canada: Benadryl, Diphenist

The FDA has issued a warning that taking higher than the recommended doses of diphenhydramine can lead to serious heart problems, seizures, coma, and even death.

How does this medication work? 

Diphenhydramine is an antihistamine that competes with histamine for H1 receptor sites relieving symptoms of allergies, hay fever and the common cold which can include itchy skin, skin rash, itchy water eyes, itchy throat, runny nose and sneezing.  Diphenhydramine can also be used to reduce nauseas, dizziness, vomiting and motion sickness.

How should I take this medication? 

Oral: Take 25 to 50mg every 4 hours (maximum: 300mg/daily).  When used for either motion sickness or insomnia, first dose should be taken 30 minutes prior to exposure.

What should I watch for while using this medication? 

Prior to starting Diphenhydramine make sure your physician is aware of any allergies or medications you currently take, if your work requires mental alertness such as operating machinery or driving.  Diphenhydramine should be used with caution in patients with asthma, cardiovascular disease, elevated intraocular pressure, prostatic hyperplasia/urinary obstruction, pyloroduodenal obstruction, thyroid dysfunction.  Diphenhydramine is contraindicated in neonates and premature infants.

What if I miss a dose?

If you miss a dose of medication, try to take it as soon as possible.  However, if it is almost time for your next dose, take only that scheduled dose.  Do not take double or extra doses.

How should I store this medication?

Keep out of the reach of children at all times.  Store at room temperature, 59 to 86° F (15 to 30° C).  Protect from light.  Keep the container tightly closed.  Properly dispose of any unused medication after the expiration date.

What are the possible side effects of using this medication? 

Chest tightness, hypotension, palpitations, tachycardia, ataxia, chills, confusion, dizziness, euphoria, fatigue, headache, nervousness, irritability, neuritis, paradoxical excitation, restlessness, sedation, seizure, vertigo, skin rash, photosensitivity, diaphoresis, constipation, diarrhea, dry mucous membranes, difficulty urinating, urinary retention, tremor, blurred vision, diplopia, nasal congestion, pharyngeal edema, wheezing.

Note this is not a complete list of side effects for Diphenhydramine, only common ones.