The drugs have a lot in common, but they also have some differences that may make one a better choice for you.
This article compares Allegra, Claritin, and Zyrtec with each other and with older antihistamines, looks at how quickly they work, their dosages and side effects, and who shouldn’t take them. In addition, it details how these medications might be used during pregnancy at the discretion of a person’s physician.
Second-Generation Antihistamines
Claritin, Zyrtec, and Allegra are all considered second-generation antihistamines. They relieve allergy symptoms with a minimal risk of side effects.
Exposure to an allergen such as pet dander, dust mites, pollen, or peanuts prompts the immune system to release chemicals called histamines.
Histamines cause allergy symptoms such as:
Congestion Runny nose Watery and itchy eyes Itchy throat Hives (urticaria)
Antihistamines work by blocking histamines and calming your allergic response.
Second-generation antihistamines work better and stay in effect for longer. They’re also much less likely to cause side effects than first-generation antihistamines—especially when it comes to making you tired.
First-Generation Antihistamines
First-generation antihistamines include older drugs such as:
Benadryl (diphenhydramine) Atarax (hydroxyzine) Chlor-Trimeton (chlorpheniramine) Clistin (carbinoxamine) Tavist (clemastine) Dimetapp/Dimetane (brompheniramine)
These medications are effective at treating allergies, but they’ve fallen out of favor because they can sedate you. In fact, some of them are also marketed as sleep aids and added to multi-symptom nighttime cold and flu products.
Third-Generation Antihistamines
Third-generation antihistamines are chemically related to second-generation medications but are considered safer and/or more effective.
They include:
Xyzal (levocetirizine)Clarinex (desloratadine)
Side Effects
All three second generation antihistamines may cause side effects such as:
Blurred visionConfusionDifficulty urinating DizzinessDrowsinessDry mouthMood changes (mostly limited to some children)Nausea and vomiting
This said, the side effect profile may vary slightly.
For instance:
Allegra is completely non-sedating (doesn’t make people sleepy)Claritin is minimally sedating (makes only a small number of people sleepy)Zyrtec causes sedation in about one in six people who take it. Patients who are over 60 years old may be more likely to experience sedation,
Dosage
You should consult your healthcare provider about the best way to take any medication, but there are standard dosing recommendations for all three of these antihistamines.
All of these antihistamines are indicated for adults and children 2 years old and older, with Zyrtec and Claritin dosed once a day for people of all ages.
Allegra is dosed twice a day for children ages 2 to 11 and once a day for adults and children ages 12 and older. Allegra can be used in children as young as 6 months old.
Effectiveness and Speed of Relief
Besides dosing, there are some slight differences in how quickly or how well the drugs work. Zyrtec and Allegra work quickly for the treatment of allergic rhinitis and hives, typically within less than an hour. Claritin may take a little longer.
All three medications can treat hives and hat fever as well.
Allegra vs. Zyrtec vs. Claritin
For mild to moderate allergy symptoms, Allegra may be preferable since the other drugs are more sedating. Yet for severe symptoms that are interfering with work, school, or play, a medication such as Zyrtec may be needed. It all depends on how much symptom relief you need and the degree of side effects you can tolerate.
Note that people may react differently to these drugs. For example, many people do not experience any fatigue on Zyrtec. Likewise, some people do experience fatigue on Allegra.
Pregnancy and Lactation
Claritin and Zyrtec have an overall good safety profile in pregnancy, though research is limited.
Similarly, Zyrtec and Claritin are preferred in lactation over Allegra.
Summary
Claritin, Zyrtec, and Allegra are all good antihistamine options and are generally well-tolerated by many people. But there are some differences between them that may make one of these antihistamines better for you than the others.
For example, Zyrtec and Allegra may work faster than Claritin. Zyrtec and Claritin can make you sleepy, while Allegra usually won’t. If you’re unsure of which antihistamine to select, consult your healthcare provider or pharmacist.
A Word From Verywell
If you find that you cannot get symptom relief from any OTC allergy medication, consider seeing an allergist—someone who specializes in diagnosing and treating allergies. They can determine the next steps, which may include allergy shots.
