Diphenhydramine: Uses, Dosage, Side Effects and More

Introduction: What is Diphenhydramine?

If you're looking for relief from allergy symptoms, common cold discomfort, motion sickness, or occasional sleeplessness, your pharmacist or doctor might recommend Diphenhydramine. This widely available over-the-counter antihistamine works by blocking the action of histamine, a substance in the body that causes allergic symptoms. It is also effective in treating motion sickness, inducing sleep, and alleviating certain symptoms of Parkinson's disease. This guide provides a comprehensive overview of diphenhydramine, covering its uses, recommended dosages, potential side effects, drug interactions, and frequently asked questions.

Uses of Diphenhydramine

Diphenhydramine is approved for several medical uses, including:

1. Allergy Relief: It helps alleviate symptoms such as sneezing, runny nose, itchy or watery eyes, and itching of the throat or nose.
2. Cold Symptoms: It can relieve symptoms associated with the common cold, such as sneezing and runny nose.
3. Motion Sickness: Diphenhydramine is effective in preventing and treating nausea, vomiting, and dizziness caused by motion sickness.
4. Insomnia: Due to its sedative properties, it is often used as a short-term treatment for sleep difficulties.
5. Parkinson's Disease symptoms (adjunctive/off-label): It can sometimes be used to help manage symptoms such as tremors and muscle stiffness, particularly in drug-induced parkinsonism or as an adjunct therapy for milder symptoms of idiopathic Parkinson's disease.

How It Works

Diphenhydramine works by blocking the H1 histamine receptors in the body. Histamine is a chemical released during allergic reactions, leading to symptoms like itching, swelling, and mucus production. By inhibiting histamine's action, diphenhydramine reduces these allergic symptoms. Additionally, it crosses the blood-brain barrier, which contributes to its sedative effects, making it useful for treating insomnia and motion sickness.

Dosage and Administration

The dosage of diphenhydramine varies based on the age of the patient and the condition being treated:

• Adults: The typical dose for allergy relief is 25-50 mg taken every 4-6 hours as needed, not exceeding 300 mg per day.
• Children (6-12 years): The recommended dose is 12.5-25 mg every 4-6 hours, not exceeding 150 mg per day.
• Children under 6 years:
  • Children under 2 years: Should not be used.
  • Children aged 2-6 years: Dosage should be determined by a healthcare provider, and generally used with caution due to increased sensitivity to side effects.

Diphenhydramine is available in various forms, including:

• Tablets: Oral administration.
• Liquid: Measured doses for easier consumption, especially in children.
• Injectable: Administered by healthcare professionals in specific medical situations (e.g., severe allergic reactions, acute dystonic reactions).

Side Effects of Diphenhydramine

Common side effects include:

• Drowsiness
• Dizziness
• Dry mouth
• Blurred vision
• Constipation

Serious side effects may include:

• Difficulty breathing (especially in individuals with respiratory conditions)
• Swelling of the face, lips, or throat (signs of a severe allergic reaction)
• Fast or irregular heartbeat
• Severe dizziness or fainting
• Confusion or hallucinations (more common in the elderly or with high doses)

If any serious side effects occur, seek medical attention immediately.

Drug Interactions

Diphenhydramine can interact with several medications and substances, including:

• Alcohol: Significantly increases drowsiness and sedation. Avoid concomitant use.
• Other Antihistamines: May enhance sedative and anticholinergic side effects.
• Sedatives and Tranquilizers: (e.g., benzodiazepines, opioids, sleep medications) – Increased risk of severe sedation and respiratory depression. Use with extreme caution and under medical advice.
• MAO Inhibitors (Monoamine Oxidase Inhibitors): Can lead to severe, potentially life-threatening side effects due to increased anticholinergic effects. Avoid using together.

Always inform your healthcare provider about all medications and supplements you are taking.

Benefits of Diphenhydramine

The clinical and practical advantages of diphenhydramine include:

• Rapid Relief: Provides quick relief from allergy symptoms.
• Multi-Use: Effective for various conditions, including allergies, insomnia, and motion sickness.
• Over-the-Counter Availability: Easily accessible without a prescription.
• Established Safety Profile: Long history of use with well-documented effects and side effects.

Contraindications of Diphenhydramine

Certain individuals should avoid using diphenhydramine, including:

• Children under 2 years of age.
• Pregnant or Nursing Women: Consult a healthcare provider before use.
• Individuals with Glaucoma: Especially narrow-angle glaucoma, as it may worsen symptoms.
• Prostate Enlargement: Can exacerbate urinary retention in men with prostate enlargement.
• Severe Liver Disease: May require dosage adjustments or avoidance due to impaired metabolism.
• Severe Respiratory Conditions: Such as acute asthma attacks, severe chronic obstructive pulmonary disease (COPD), or bronchitis, as it can thicken respiratory secretions and worsen breathing.
• Seizure Disorders: Caution is advised, as it may lower the seizure threshold in some individuals.

Precautions and Warnings

Before using diphenhydramine, consider the following precautions:

• Driving and Operating Machinery: Due to significant drowsiness, avoid driving or operating heavy machinery until you know how diphenhydramine affects you.
• Elderly Patients: Individuals over 65 are more susceptible to side effects like drowsiness, confusion, and anticholinergic effects; lower doses may be necessary and use should be carefully considered.
• Pre-existing Conditions: Inform your doctor or pharmacist if you have:
  • Asthma, chronic obstructive pulmonary disease (COPD), or other respiratory issues (as it can thicken secretions).
  • Glaucoma (especially narrow-angle glaucoma).
  • Prostate enlargement.
  • Heart disease or high blood pressure.
  • A seizure disorder.
• Alcohol and Other Sedatives: Avoid alcohol and other sedatives, as they can significantly increase drowsiness and other side effects.

FAQs

1. Can I take diphenhydramine for allergies? Yes, diphenhydramine is effective for relieving allergy symptoms.
2. Is diphenhydramine safe for children? Yes, but consult a pediatrician for appropriate dosing.
3. How long does diphenhydramine take to work? It typically starts working within 30 minutes to an hour.
4. Can I use diphenhydramine for sleep? Yes, it is often used as a short-term sleep aid.
5. What should I do if I miss a dose? Take it as soon as you remember, but skip it if it's almost time for the next dose.
6. Can I drink alcohol while taking diphenhydramine? It is not recommended, as it can increase drowsiness.
7. Is diphenhydramine addictive? No, it is not considered addictive, but misuse can lead to dependence.
8. Can I take diphenhydramine with other medications? Always consult your doctor or pharmacist to avoid interactions.
9. What are the signs of an allergic reaction to diphenhydramine? Symptoms include rash, itching, swelling, and difficulty breathing.
10. How should I store diphenhydramine? Keep it in a cool, dry place away from direct sunlight and out of reach of children.

Brand Names

Diphenhydramine is marketed under several brand names, including:

• Benadryl
• Sominex
• Nytol
• Sleepinal

Conclusion

Diphenhydramine is a versatile antihistamine with a range of uses, from allergy relief to sleep aid. While it is generally safe and effective, it is essential to use it responsibly, always considering its potential for significant drowsiness and other side effects, as well as drug interactions. Always consult with your healthcare provider or pharmacist before starting any new medication to ensure it is appropriate for your individual health needs, especially for children or the elderly.