Allegra vs Zyrtec: What's the difference?
Medically reviewed by Drugs.com. Last updated on Oct 8, 2020.
Allegra and Zyrtec are both antihistamines, but is one more effective or less likely to cause sedation than the other?
Allegra has the lowest risk of sedation out of all antihistamines so is preferred if an antihistamine is needed for people working in safety-critical jobs. Even though Zyrtec is 3.5 times more likely to cause sedation than Allegra, it is still much less sedating than some older antihistamines such as promethazine.
- Allegra works within two hours and Zyrtec works within one hour.
- Several studies have found cetirizine (Zyrtec) to be more effective than fexofenadine (Allegra) at relieving symptoms of allergic rhinitis and urticaria, and it appears to have a longer duration of action.
- Studies have not compared the effects of Allegra and Zyrtec for conditions such as postnasal drip, but research suggests intranasal antihistamines such as azelastine are more effective.
- Allegra should not be taken with grapefruit juice. Zyrtec has no reported food interactions.
- Zyrtec and Allegra should not be taken at the same time, instead, if symptoms are persisting, it is better to take another drug with a different mechanism of action.
Allegra is a brand name for the drug fexofenadine and Zyrtec is a brand name for the drug cetirizine. Both fexofenadine and cetirizine are popular antihistamines with many similarities but there are some important differences.
Which is more sedating? Allegra or Zyrtec?
Allegra (fexofenadine) and Zyrtec (cetirizine) are second-generation antihistamines. Second-generation antihistamines were first developed in the 1990s to provide allergy relief without the unwanted side effect of sedation common to first-generation antihistamines such as promethazine and diphenhydramine. However, it soon became apparent that not all second-generation antihistamines were equal when it came to not causing drowsiness or affecting other thought processes. Cetirizine is significantly more likely than fexofenadine to cause drowsiness.
Fexofenadine (Allegra), even in dosages exceeding those recommended, is the least sedating of all second-generation antihistamines, so is considered the antihistamine of choice for people in safety-critical jobs such as airline pilots.
Which is more effective for Allergic rhinitis?
Trials have shown both Allegra (fexofenadine) and Zyrtec (cetirizine) are significantly more effective than placebo (a pretend pill) for reducing symptoms associated with allergic rhinitis, hay fever, and other allergies. Trials have not consistently shown that one antihistamine is more effective than another; however, one trial reported cetirizine produced a 26% greater reduction in the number of allergic rhinitis symptoms at 12 hours and 14% greater reduction in symptoms overall compared with fexofenadine. Cetirizine also appeared more effective for symptoms such as runny nose, sneezing, itchy/watery eyes, and itchy nose, mouth or throat. Cetirizine was slightly more likely (0.8%) than fexofenadine to cause drowsiness. Another trial reported similar findings (33% greater reduction in allergic rhinitis symptoms) and also found cetirizine had a longer duration of effect.
Intranasal or ophthalmic (into the eye) antihistamines have a quicker onset of action than oral antihistamines (within about 15 minutes); however, they need to be administered several times daily. In people with allergic rhinoconjunctivitis and predominantly eye symptoms, ophthalmic antihistamines work much quicker (within 3 to 15 minutes) and are much more effective than any other form of treatment. Intranasal antihistamines are as effective as intranasal cromolyn, intranasal nedocromil, and leukotriene modifiers in seasonal allergic rhinitis; however, are not as effective at relieving nasal congestion and other symptoms as intranasal glucocorticoids.
Allegra Vs Zyrtec for urticaria and other skin reactions
All second generation antihistamines, including Allegra and Zyrtec, are effective for acute and chronic urticaria, although more trials have been conducted in people with chronic urticaria. One trial found cetirizine to be more effective than fexofenadine at relieving symptoms in 97 patients with chronic urticaria with 51.9% of participants taking cetirizine reporting themselves as symptom-free after 28 days of treatment compared with only 4.4% of participants taking fexofenadine. Partial improvement was reported by 36.5% of people assigned cetirizine (42.2% assigned fexofenadine) and 11.5% experienced no improvement with cetirizine (53.3% with fexofenadine). No difference in side effects was noted between the two.
Allegra Vs Zyrtec for Postnasal Drip
Post nasal drip may occur for various reasons - allergies (particularly to dairy), colds or flu, various drugs (including birth control pills and high blood pressure tablets), cold temperatures, bright lights, hormonal changes and spicy foods.
Thin postnasal drip secretions caused by allergies may be treated with antihistamines. Second-generation antihistamines such as Allegra and Zyrtec may offer better relief than older-type antihistamines such as promethazine (older antihistamines tend to thicken post-nasal secretions). Intranasal antihistamines, such as azelastine, have a faster onset of action (15 minutes) and appear more effective than oral antihistamines although require more frequent administration. Other treatments include decongestants, cromolyn, and corticosteroid nasal sprays.
In the treatment of post nasal drip caused by nonallergic causes, oral second-generation antihistamines are not very effective. However, the intranasal antihistamine azelastine is effective. Azelastine improves all rhinitis symptoms including nasal congestion, postnasal drip, sneezing and sleeping difficulty. The most common side effect is a metallic aftertaste; however, this is more likely at higher dosages and tends to dissipate with continued use.
Allegra Vs Zyrtec To Relieve Cold Symptoms
Second-generation antihistamines (such as Allegra and Zyrtec) have limited effectiveness at relieving symptoms of cold such as a runny nose and sneezing (only 45% of adults felt better after using them compared to 35% with placebo [a pretend pill]). Effects were only noticeable if used within the first two days of a cold, use of antihistamines made no difference thereafter.
Allegra Vs Zyrtec: Administration
The antihistamine effects of Allegra and Zyrtec last for at least 24 hours, therefore, they are both given once daily. Fexofenadine, the active ingredient of Allegra works within two hours. Cetirizine, the active ingredient of Zyrtec works within one hour.
Allegra Vs Zyrtec: Side Effects, Interactions and Price
Side effects are generally mild with second-generation antihistamines and include a headache and rarely dry mouth, and nausea. Zyrtec is 3.5 times more likely than Allegra to cause sedation; however, Zyrtec is still much less sedating than older antihistamines such as promethazine.
Side effects are generally mild with second-generation antihistamines and include a headache and rarely dry mouth, and nausea. All the second generation antihistamines currently on the market appear free from adverse cardiovascular effects. Few major interactions have been reported with either Allegra or Zyrtec; however, there is the possibility that side effects such as sedation, confusion, and mental alertness may be enhanced if given with other drugs with this side effect.
Grapefruit juice appears to decrease the rate and extent of absorption of fexofenadine (Allegra) by about 30%. Cetirizine (Zyrtec) has no reported interactions with grapefruit or grapefruit products. More studies are needed to determine if there are any interactions between second generation antihistamines and herbal products and other types of food. Always speak with your doctor of pharmacist before using any drugs in combination.
Cost is similar for 30 Allegra and 30 Zyrtec tablets and both are available as generics.
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- Hampel F, Ratner P, Mansfield L, et al. Fexofenadine hydrochloride, 180 mg, exhibits equivalent efficacy to cetirizine, 10 mg, with less drowsiness in patients with moderate-to-severe seasonal allergic rhinitis. Ann Allergy Asthma Immunol. 2003 Oct;91(4):354-61.
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