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Claritin, Allegra, and Zyrtec all belong to a class of medication known as antihistamines. These medications are mainly used to treat allergies, including seasonal allergies or hay fever (allergic rhinitis).
When your body has an allergic reaction, your immune system releases a chemical messenger called histamine. Histamine binds to specific immune cells and triggers the classic allergy symptoms of itching, runny nose, sneezing, etc. Antihistamines prevent histamine from attaching to the cells and keep your allergy symptoms in check. This group of medications is often classified based on its drug generation.
- First-generation antihistamines, like Benadryl, are effective against seasonal allergies but can make you very sleepy.
- Newer generation antihistamines are preferred because they work against seasonal allergies but don’t cause as much drowsiness or sedation.
- Newer generation antihistamines include Claritin (active ingredient loratadine), Allegra (active ingredient fexofenadine), and Zyrtec (active ingredient cetirizine).
- Of the newer generation antihistamines, Zyrtec has the highest risk of drowsiness, Claritin is the slowest to start working, and you should not take Allegra with fruit juice.
First-generation antihistamines include common medications like diphenhydramine, the active ingredient in Benadryl. First-generation antihistamines are effective at treating allergy symptoms, but they can cause significant sedation (drowsiness)—this makes them less useful for people suffering from seasonal allergies who can’t spend all day in bed. Fortunately, newer antihistamine generations (second- and third-generations) cause less drowsiness while still maintaining effectiveness. These newer generations include the active ingredients loratadine (found in Claritin), fexofenadine (found in Allegra), and cetirizine (Zyrtec). While all are effective, the differences may affect which one is right for your allergy symptoms.
What is Claritin?
The active ingredient of Claritin is loratadine. This drug generally does not cause drowsiness and can last for 24 hours (UpToDate, 2020). However, it may take 75 minutes to take effect (Tenn, 2018). Claritin is effective against nasal and eye allergy symptoms, like sneezing, runny or itchy nose, and itchy, watery eyes (Tenn, 2018). It can be used to treat seasonal allergies in children as young as two years old. Claritin comes in either 24-hour or 12-hour doses; available forms include tablets, quick-dissolving tablets, liquid gels, syrup, and chewable tablets. Headache is the most common side effect reported. Others include drowsiness, dry mouth, nosebleeds, sore throat, difficulty falling asleep or staying asleep, nervousness, stomach pain, diarrhea, and red or dry eyes (MedlinePlus, 2018)
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What is Allegra?
The active ingredient of Allegra is fexofenadine. This drug generally does not cause drowsiness—in fact, it has the least reported frequency of drowsiness or sedation of the newer generation antihistamines. Like the others, its effects can last for 24 hours (Howarth, 1999), and it can start working in one hour after the first dose (Allegra, n.d.). Allegra helps improve the symptoms of sneezing, runny nose, itchy nose/mouth/throat, and itchy, watery, or red eyes. It can be used to treat seasonal allergies in children as young as two years old. Allegra comes in either 24-hour or 12-hour doses; available forms include tablets, gelcaps, quick-dissolving tablets, and syrup. Headache is the most common side effect reported; others include dizziness, diarrhea, vomiting, pain in the arms, legs, or back, pain during menstrual periods, and cough (MedlinePlus, 2017).
What is Zyrtec?
The active ingredient of Zyrtec is a newer generation antihistamine, cetirizine. This drug is generally nonsedating but did cause drowsiness in 14% of people in clinical trials—not as much as the first-generation antihistamines (Zyrtec, n.d.). Zyrtec is effective against seasonal allergy symptoms like runny nose, itchy eyes, nasal congestion, sneezing, hives, allergic rhinitis, etc. Zyrtec begins working within the first hour after taking it and can last 24 hours (Day, 2001). It can be used to treat seasonal allergies in children as young as two years old. It is available in tablets, syrup, dissolving tablets, and liquid gels. Other than drowsiness in some people, other side effects of Zyrtec include headaches, dry mouth, stomach pain, or vomiting (MedlinePlus, 2018). There is another antihistamine available over the counter that you may have heard about: Xyzal. The active ingredient in Xyzal is levocetirizine. If you look closely, the active ingredient in Xyzal looks like that of Zyrtec, cetirizine—that is because the compounds are similar. Xyzal is formulated with a different form of cetirizine, called levocetirizine.
Comparing Claritin, Allegra, and Zyrtec
|Characteristic||Claritin (loratadine)||Allegra (fexofenadine)||Zyrtec (cetirizine)|
|Starts working in an hour||No||Yes||Yes|
|Level of drowsiness||Low||None||Low to Medium|
|Effective for seasonal allergy symptoms||Yes||Yes||Yes|
|Lasts 24 hours||Yes||Yes||Yes|
|Children’s doses available (over age 2)||Yes||Yes||Yes|
|Interaction with food||No||Yes- do not take with fruit juice||No|
|Use with alcohol||No||No||No|
There are many different options for treating allergies, even within a single medication class like antihistamines. In the end, it depends on which medication works best for you and has the least side effects. Talk to your healthcare provider about your symptoms, and together you can decide on the option that is right for you.