Allegra (Fexofenadine) vs Other Antihistamines: Complete Comparison

Key Takeaways

• Allegra (fexofenadine) offers fast, non‑sedating relief for hay fever and hives, with a 24‑hour duration.
• Claritin (loratadine) and Zyrtec (cetirizine) are the closest rivals, differing mainly in onset speed and mildness of drowsiness.
• Xyzal (levocetirizine) is the most potent third‑generation antihistamine but can cause slightly more sleepiness.
• Benadryl (diphenhydramine) provides strong relief but is highly sedating and best reserved for night‑time or short‑term use.
• Choose based on how quickly you need relief, how much drowsiness you can tolerate, and whether you need prescription strength.

When allergy season rolls around, the shelves are packed with names like Allegra, Claritin, Zyrtec and Xyzal. Deciding which one actually works for you can feel like a gamble. This guide walks through the science, the practical differences, and the real‑world pros andcons so you can pick the right antihistamine without guessing.

How Antihistamines Work

All the drugs we’ll discuss belong to the antihistamine class. They block histamine, a chemical released by mast cells when you encounter an allergen such as pollen, pet dander or certain foods. Histamine binds to H1 receptors in the nose, eyes, skin and lungs, causing itching, swelling, sneezing and watery eyes. By occupying those receptors, antihistamines prevent the symptoms from developing.

Modern antihistamines are divided into two generations. First‑generation agents (e.g., diphenhydramine) cross the blood‑brain barrier and often cause drowsiness. Second‑ and third‑generation drugs (e.g., fexofenadine, levocetirizine) are designed to stay out of the brain, delivering relief without pulling the plug on alertness.

Decision Criteria - What Really Matters

Before we dive into brand‑by‑brand details, here are the key factors most people consider:

1. Onset of action: How fast you feel relief after the first dose.
2. Duration of effect: How long one dose controls symptoms.
3. Sedation potential: Whether you can stay focused at work or school.
4. Side‑effect profile: Headaches, dry mouth, or gastrointestinal upset.
5. Dosage flexibility: Availability of tablets, chewables, or liquid forms.
6. Cost & availability: OTC versus prescription and price per dose.

We’ll rate each drug against these criteria to give you a clear picture.

Allegra (Fexofenadine) - The Benchmark

Allegra is a second‑generation antihistamine whose active ingredient is fexofenadine hydrochloride. Approved by the FDA in 1996 and by the MHRA in the UK in 1997, it quickly became the go‑to for non‑sedating allergy relief.

• Typical dose: 180mg once daily for adults; 60mg twice daily for children 6‑11years.
• Onset: 1‑2hours after ingestion.
• Duration: Up to 24hours, making once‑daily dosing convenient.
• Sedation: Minimal; < 1% of users report noticeable drowsiness.
• Metabolism: Not processed by CYP450 enzymes, so drug‑drug interactions are rare.
• Cost (UK, 2025): £7.99 for a pack of 30 tablets (OTC).

Because it stays out of the brain, Allegra is popular with professionals, students and drivers who can’t afford a nap after a dose.

Claritin (Loratadine) - The Close Competitor

Claritin contains loratadine, another second‑generation antihistamine introduced in 1993. It shares many of Allegra’s non‑sedating qualities but differs in a few practical ways.

• Typical dose: 10mg once daily for adults and children over 6years.
• Onset: 1‑3hours.
• Duration: 24hours.
• Sedation: Low; about 2‑3% notice mild sleepiness.
• Metabolism: Processed by CYP3A4; can interact with certain antifungals or macrolide antibiotics.
• Cost (UK, 2025): £5.50 for 30 tablets (OTC).

Claritin is a solid all‑rounder, especially when you want a cheap, over‑the‑counter option that still won’t knock you out.

Zyrtec (Cetirizine) - The Fast‑Acting Option

Zyrtec is built on cetirizine, a second‑generation antihistamine that hit the market in 1995. Its claim to fame is a quicker onset compared with Allegra and Claritin.

• Typical dose: 10mg once daily for adults; 5mg once daily for children 2‑5years.
• Onset: 30‑60minutes - the fastest among the non‑sedating set.
• Duration: 24hours.
• Sedation: Slightly higher - about 5‑7% report mild tiredness.
• Metabolism: Mostly CYP3A4, with a small renal excretion component.
• Cost (UK, 2025): £6.20 for 30 tablets (OTC).

If you need relief within an hour of exposure-say, before stepping onto a pollen‑heavy balcony-Zyrtec is a go‑to.

Xyzal (Levocetirizine) - The Potent Third‑Generation Choice

Xyzal delivers levocetirizine, the active enantiomer of cetirizine, launched in 2007. It’s marketed as the most potent with a similar safety profile.

• Typical dose: 5mg once daily for adults and children over 12years.
• Onset: 45‑60minutes.
• Duration: 24hours.
• Sedation: Low but a notch higher than Allegra (≈4% report drowsiness).
• Metabolism: Primarily hepatic via CYP3A4; caution with strong inhibitors.
• Cost (UK, 2025): £9.50 for 30 tablets (OTC).

People who have tried other antihistamines without full relief often turn to Xyzal for its extra punch.

Benadryl (Diphenhydramine) - The Classic Sedating Option

Benadryl contains diphenhydramine, a first‑generation antihistamine introduced in the 1940s. It works well but pulls the curtain on alertness.

• Typical dose: 25‑50mg every 4‑6hours for adults; 12.5‑25mg for children 6‑12years.
• Onset: 15‑30minutes - the fastest of the lot.
• Duration: 4‑6hours, requiring multiple doses.
• Sedation: High; up to 70% report drowsiness.
• Metabolism: CYP2D6 and CYP3A4 pathways.
• Cost (UK, 2025): £4.00 for 30 tablets (OTC).

Benadryl shines for short‑term, nighttime, or severe itching when you don’t mind feeling sleepy.

Direct Comparison Table

Which Antihistamine Is Right for You?

Below is a quick‑read guide that matches common scenarios to the best‑fit drug.

• Need all‑day, non‑sedating relief for work or school? Allegra or Claritin-both give 24‑hour coverage with virtually no drowsiness.
• First dose while outdoors - want results within an hour? Zyrtec is the fastest non‑sedating option; Xyzal is a close second.
• Allergy symptoms that haven’t responded to other OTCs? Try Xyzal; its higher receptor affinity often breaks through partial resistance.
• Severe itching at night and you don’t mind sleeping? Benadryl provides rapid, strong relief and doubles as a sleep aid.
• Budget‑conscious, occasional allergy attacks? Claritin is the cheapest non‑sedating choice; Benadryl is the cheapest overall if sedation isn’t an issue.

Practical Tips & Common Pitfalls

Even the best drug can fall flat if you ignore a few simple rules.

1. Take with water, not fruit juice. Citrus juices (especially grapefruit) can reduce the absorption of fexofenadine and loratadine.
2. Mind the half‑life. Fexofenadine’s half‑life is about 14hours, so missing a dose can leave a gap; with Benadryl, timing is critical because the effect fades after 4‑6hours.
3. Watch for drug interactions. While Allegra is low‑risk, loratadine and cetirizine can interact with strong CYP3A4 inhibitors (e.g., ketoconazole). Always check with your pharmacist.
4. Consider age‑specific formulations. Chewable tablets or syrups are available for children, but dosing varies - never double‑up adult tablets for a kid.
5. Pregnancy & breastfeeding. Most antihistamines are Category B, but fexofenadine should be used only if clearly needed. Discuss with a GP.

Frequently Asked Questions

Whether you’re battling spring pollen, summer grass, or a sudden bout of hives, the right antihistamine can keep you comfortable without derailing your day. Use the criteria, table, and scenario guide above to match your lifestyle and symptom profile. And remember: if over‑the‑counter options don’t bring relief, a quick chat with your GP can open the door to prescription‑strength alternatives.