Diphenhydramine

Uses	Allergic Symptoms
Therapy	Cough Cold Preparation
Side Effects	Tiredness, Dry Mouth, Dizziness, Sleepiness

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Molecule Description

Diphenhydramine is an anti-allergic medicine widely used for the treatment of running nose, itching, sleeplessness, skin rashes, insect bites, etc.

Uses

Sleep disturbances (insomnia)
Allergic reactions
Sickness, vomiting and ear disturbances, especially on traveling in automobiles, airplanes, etc. (motion sickness)
Movement abnormalities, tremors, muscle stiffness, impaired speech (parkinsonism)
Cough (in adolescents and adults above 12 years)

Contraindications

When should one not use Diphenhydramine

Allergy to Diphenhydramine or any of the components of the tablet
Lung problems (asthma, etc.)
A genetic disorder that causes accumulation of proteins required to make red blood cells (porphyria)

Side effects

Common side effects of this drug are:

Headache
Dry mouth
Rashes
Decreased red blood cells and platelets (anemia and thrombocytopenia)
Confusion, feeling dizzy
Feeling sick, sleeplessness (insomnia), fatigue
Weight loss
Stomach pain
Retention of urine
Lung infections

Precautions and Warnings

Pregnancy

Diphenhydramine can be used in pregnancy but it is recommended to be cautious as it may cause drowsiness and decreased blood cell counts. If you are pregnant, consult your doctor before taking this medicine.

Breast Feeding

Diphenhydramine is secreted in breast milk and is maybe harmful for infants. Hence do not breastfeed your baby while using this medicine.

Driving

Do not drive while taking Diphenhydramine. This medicine may lead to sleepiness or drowsiness soon after you take a dose.

Alcohol

The use of alcohol, along with Diphenhydramine, is not recommended since the combination increases the risk of side-effects like dizziness and drowsiness.

Other General Warnings

Talk to your doctor if

High blood pressure
Asthma
Thyroid problems
Raised pressure in the eye (glaucoma)
Enlarged prostate
Urinary tract obstruction

Mode of Action

How Does It Work?

Histamines are chemicals secreted by the immune system in response to any reaction or allergy. They cause symptoms such as itching, sneezing, rashes, running nose, etc. Diphenhydramine works by blocking natural histamine that is produced by our immune system.

Interactions

Interactions with other medicines

Chlorpheniramine (Avil – a medicine to treat certain allergies)
Zolpidem (used to treat anxiety)
Cephalothin (antibacterial)
Amphotericin (antifungal)
Hydrocortisone (used to treat allergic reactions)
Certain medicines used to treat anxiety, seizures (Barbiturates – Phenobarbital, etc.)

Interactions with food items

Avoid alcohol beverages with Diphenhydramine because it can increase the brain and nervous system side effects.

Dosage

Overdose

Accidental overdose will cause more drowsiness and may not be harmful. But high overdose can cause symptoms such as fever, reddened skin, agitation, tremors, etc. that may require medical attention. Inform your doctor immediately in the presence of any such symptoms.

Missed a Dose

Take the missed dose as early as you remember. Skip the missed dose and do not take extra medicine to compensate for the missed dose.

Frequently Asked Questions (FAQs)

Diphenhydramine is available as over the counter medicine and can be bought at convenience. But you are advised not to take the medicine without a prescription. If you have a minor complaint which does not require you to visit a doctor, do not use it for more than 2 weeks. Diphenhydramine causes some unwanted effects which can be harmful. Hence, it is not recommended for long-term usage without supervision.

Diphenhydramine is predominantly an anti-allergic. It can help with your sleep if used occasionally. But, regular daily usage as a sleeping pill is not recommended as it may cause some potential side effects which can be dangerous for you.

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References:

Medscape. Diphenhydramine. [Accessed on 15 Jun, 2026].(Online)

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