Antihistamines: Everything You Need to Know

Here is a complete overview of antihistamines.

What Are Antihistamines?
Antihistamines are medications that block the effects of histamine, a chemical your body releases during an allergic reaction. They are commonly used to relieve symptoms like sneezing, itching, watery eyes, and runny nose.

Types of Antihistamines
Antihistamines are divided into two main categories: first-generation and second-generation.

First-Generation Antihistamines
These older medications are effective but often cause drowsiness because they cross the blood-brain barrier. Examples include:

  • Diphenhydramine (Benadryl)

  • Chlorpheniramine (Chlor-Trimeton)

  • Doxylamine (Unisom)

Second-Generation Antihistamines
These newer medications are less likely to cause drowsiness and are preferred for long-term use. Examples include:

  • Loratadine (Claritin)

  • Cetirizine (Zyrtec)

  • Fexofenadine (Allegra)

 

User Ratings of Antihistamine Effectiveness

Here are average user effectiveness ratings for common antihistamines (oral and nasal sprays), ordered from highest to lowest:

  • Azelastine (nasal spray): 4.5/5

  • Fexofenadine (oral): 4.3/5

  • Cetirizine (oral): 4.2/5

  • Olopatadine (nasal spray): 4.1/5

  • Loratadine (oral): 4.0/5

  • Diphenhydramine (oral): 3.8/5

  • Chlorpheniramine (oral): 3.6/5

(Ratings based on aggregated user feedback from health platforms.)

Common Uses of Antihistamines
Antihistamines are primarily used to treat:

  • Seasonal allergies (hay fever)

  • Food allergies

  • Hives (urticaria)

  • Insect bites or stings

  • Motion sickness (some first-generation types)

Recommended Dosages
Dosages vary by medication and age group. Always follow your doctor’s advice or the label instructions. Here are general guidelines:

  • Diphenhydramine (Benadryl): 25–50 mg every 4–6 hours (adults)

  • Loratadine (Claritin): 10 mg once daily (adults)

  • Cetirizine (Zyrtec): 5–10 mg once daily (adults)

  • Fexofenadine (Allegra): 60 mg twice daily or 180 mg once daily (adults)

For children, consult a pediatrician for appropriate dosing.

Potential Side Effects
Side effects depend on the type of antihistamine:

  • First-generation: Drowsiness, dry mouth, dizziness, blurred vision

  • Second-generation: Mild drowsiness (rare), headache, nausea

Serious side effects (e.g., rapid heartbeat, difficulty urinating) are rare but require immediate medical attention.

Who Should Avoid Antihistamines?
Certain individuals should use antihistamines with caution or avoid them altogether:

  • Pregnant or breastfeeding women (consult a doctor first)

  • People with glaucoma, enlarged prostate, or heart conditions

  • Those taking sedatives or tranquilizers (risk of increased drowsiness)

Where to Buy Antihistamines
Antihistamines are widely available over-the-counter (OTC) at pharmacies, grocery stores, and online retailers. Here are some purchase options:

Always check expiration dates and ensure the product is sealed.

Natural Alternatives to Antihistamines
For those seeking non-pharmaceutical options, consider:

  • Quercetin (a natural antihistamine found in apples and onions)

  • Butterbur (a herbal supplement)

  • Nasal saline rinses (to flush out allergens)

Note: Natural remedies may not be as effective for severe allergies.

Final Tips for Using Antihistamines Safely

  • Start with the lowest effective dose.

  • Avoid alcohol when taking sedating antihistamines.

  • Monitor for side effects, especially in children and older adults.

  • Consult a doctor if symptoms persist or worsen.

By understanding how antihistamines work and using them responsibly, you can effectively manage allergy symptoms and improve your quality of life.