How do Claritin and Allegra work?
Claritin (loratadine) and Allegra (fexofenadine) are both second-generation antihistamines that block H1 receptors to reduce allergy symptoms like sneezing, runny nose, itching, and hives. They don't cross the blood-brain barrier much, so they cause less drowsiness than first-generation options like Benadryl.[1]
Key differences in effectiveness and use
Claritin starts working in 1-3 hours and lasts 24 hours, approved for allergies, hives, and itching in adults and kids over 2 (or 6 months for syrup). Allegra kicks in faster—within 1 hour—and also lasts 24 hours, but it's approved for similar uses plus some non-drowsy relief for chronic hives. Studies show similar overall effectiveness for seasonal allergies, though Allegra may edge out for nasal symptoms in some people.[1][2]
| Feature | Claritin (loratadine) | Allegra (fexofenadine) |
|---------|-----------------------|------------------------|
| Active ingredient | Loratadine (10 mg standard dose) | Fexofenadine (60 mg or 180 mg) |
| Time to onset | 1-3 hours | ~1 hour |
| Duration | 24 hours | 24 hours |
| Forms | Tablets, liquids, disintegrating tabs, RediTabs | Tablets, liquids, ODT, capsules |
| Approved ages | 2+ years (syrup: 6 months+) | 6 months+ |
Side effects and drowsiness risk
Both are non-sedating for most users. Claritin has rare side effects like headache (12%), fatigue (4%), dry mouth. Allegra lists headache (13%), nausea (5%), dizziness; it can cause drowsiness in ~2% of cases. Neither impairs driving much, unlike older antihistamines.[1][2]
Interactions and restrictions
Claritin metabolizes via liver enzymes, so avoid with strong CYP3A4 inhibitors like ketoconazole. Allegra is excreted via kidneys and interacts with fruit juices (orange, grapefruit, apple)—they cut absorption by 30-50%—and antacids with aluminum/magnesium. Take Allegra on an empty stomach, away from juices.[1][2]
Cost and availability
Both are over-the-counter generics, so prices are low: ~$10-20 for 30-day supply. Store brands match name brands. No major patent issues now—Claritin's key patents expired in 2002, Allegra's in 2010-2011.1
Which one to choose?
Depends on your needs: Allegra if you want faster relief or avoid juices/antacids; Claritin if cost or kid-friendly forms matter more. Neither cures allergies—pair with nasal sprays if needed. Consult a doctor for severe cases or pregnancy.[1][2]
[1]: FDA labels via Drugs.com (Claritin: https://www.drugs.com/claritin.html; Allegra: https://www.drugs.com/allegra.html)
[2]: Mayo Clinic comparison (https://www.mayoclinic.org/diseases-conditions/allergies/in-depth/allergy-medications/art-20047403)