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Key takeaways
There are no known interactions between Allegra and Zyrtec.
While it’s probably safe to combine Allegra and Zyrtec, this will not provide the benefits users want since the two work similarly.
Taking both Allegra and Zyrtec can also cause side effects, such as drowsiness and dry mouth. The side effects can be more serious for people with other medical conditions, such as heart disease.
Take either Allegra or Zyrtec, whichever one works better for you, daily as needed. If that’s not enough, consider adding immunotherapy or a nasal steroid spray. The latter can be available over-the-counter or as a prescription drug.
Antihistamines are a common oral tablet choice during allergy season or after an allergic reaction. Dealing with common symptoms of allergies, such as a runny nose, nasal congestion, itchy skin, watery eyes, and sneezing, can be bothersome. Antihistamines are allergy medicines that reduce those symptoms by blocking histamines.
Allegra (fexofenadine) and Zyrtec (cetirizine) are two examples of newer antihistamines. While they’re different medicines, they work the same (for the most part). While probably okay, taking both won’t be helpful and can lead to a serious risk of side effects. Patients should not take these over-the-counter allergy medications on the same day unless advised to by a healthcare provider.
Can you take Allegra and Zyrtec together?
When someone is battling a bad case of hay fever, taking Allegra and Zyrtec together can be tempting. And to be fair, no interactions between the two have been found. However, people probably shouldn’t take the two together. It’s simply not a good idea to mix allergy medications.
“While there’s generally no harmful drug interaction between Allegra and Zyrtec, it’s usually not the best approach for managing allergies,” says Dr. Kara Wada, MD, a board-certified pediatric and adult allergy, immunology, and lifestyle medicine physician at Ohio State University and Wexner Medical Center.
This is true for a few reasons.
They work similarly
Allegra and Zyrtec are second-generation antihistamines that block histamine receptors to reduce allergy symptoms, notes Dr. Jenna Podjasek, MD, an allergist/immunologist, writer, and Mayo Clinic alumnus.
“For typical allergy symptoms, there is generally no additional benefit to taking both Allegra and Zyrtec at the same time,” she says.
There’s a risk of stronger side effects
Independently, antihistamines can cause people to feel drowsy or experience dry mouth, just to name a couple of symptoms. So, when you take two of them, you may feel those side effects even more, according to Dr. Wada.
RELATED: Does Zyrtec raise blood pressure?
One might not work as well for someone
While these two medications are similar, they do have differences. Dr. Wada says Zyrtec can help more with skin itching, while Allegra is less likely to cause drowsiness.
“The choice between them usually depends on how well an individual responds to either medication or the side effects of that medication,” Dr. Podjasek adds.
What works well for one person might not be what works well for another. “The best choice depends on your specific needs and should be discussed with your medical team,” Dr. Wada concludes.
You can alternate Allegra and Zyrtec, taking a different one each day, Dr. Podjasek says, but that doesn’t mean it will necessarily be beneficial. Instead, she encourages picking one of the two to use. “Some patients find that one medication works better for them than the other, and we typically recommend patients stick with the one that improves symptoms without causing side effects.”
Combining an antihistamine with an intranasal corticosteroid is often more effective to reduce allergic rhinitis symptoms.
Can I take Allegra in the morning and Zyrtec at night?
If someone’s healthcare professional prescribes taking Allegra in the morning and Zyrtec at night, that’s fine. Otherwise, the answer is the same: Taking two antihistamines in one day isn’t a great idea.
“Taking Allegra in the morning and Zyrtec at night could provide enough time between doses, as both medications have different half-lives and durations of action. However, there is generally no need to take both for typical allergy symptoms,” Dr. Podjasek says.
If you’ve tried them both separately and neither one is cutting it, consider adding something that’s not an antihistamine. “There are many other treatment options available, such as nasal sprays or allergen immunotherapy,” she continues. “As always, consult with your healthcare provider before making any changes to your medications.”
Additionally, air purifiers are an example of a preventive at-home treatment worth considering.
Dr. Wada agrees that while 24 hours is technically long enough, a patient’s best bet is to talk to their doctor. That’s not only because taking two can increase the risk of potential side effects but also for ease. “Generally, taking one effective antihistamine is simpler and less expensive,” she says. “However, the greater issue is whether taking both on the same day is beneficial at all (as explained above).”
How do Allegra and Zyrtec work?
The mechanism of action for Allegra and Zyrtec, both over-the-counter (OTC) oral antihistamines, is largely the same: They block the effects of histamines in the body to reduce allergy symptoms. Both are also usually taken short-term, seasonally, or as needed. On the other hand, people will want to avoid fruit juices, such as grapefruit juice, apple juice, and orange juice, as these can make the drug less effective.
The usual dose of Allegra for an adult is 180 mg, while the usual dose of Zyrtec for an adult is 5 to 10 mg. For children, a Zyrtec dose ranges from 2.5 mg to 10 mg; an Allegra dosage ranges from 30 mg to 60 mg every 12 hours.
When it comes to which works faster, the answer is Zyrtec. While Allegra kicks in within two hours, Zyrtec kicks in after only one. According to one study, Zyrtec was more effective in relieving allergy symptoms. But Zyrtec may be more likely to cause drowsiness. There are pros and cons to both drugs.
Most importantly, though, when deciding which antihistamine to take, have a pharmacist or allergy doctor assess your medical history, current medications, and other concerns first. While Zyrtec works better for some people, Allegra works better for others.
RELATED: Allegra vs. Zyrtec: Differences, similarities, and which one is better for you
Side effects of mixing Allegra and Zyrtec
If someone does take both Allegra and Zyrtec, they may experience more side effects, according to Dr. Podjasek. She lists drowsiness, dry mouth, and a headache as examples.
Dr. Wada lists dry eyes and warns more about the drowsiness effect. “This could be more pronounced, affecting your ability to drive or work safely, especially if you’re sensitive to antihistamines.”
That might be surprising since Allegra and Zyrtec are second-generation antihistamines and should be less likely to cause such side effects. Dr. Podjasek explains, “Although both drugs are less likely to cause drowsiness compared to first-generation antihistamines, such as Benadryl, the combined effects may lead to increased sedation in some people.”
Her particular warning applies to people with heart problems, though. She says excessive antihistamine intake can (rarely) result in cardiac issues, such as arrhythmias. As always, the presence of other medical problems should be considered when trying a new medication, even if it’s an OTC allergy medication.
The bottom line
While taking Allegra and Zyrtec together isn’t necessarily unsafe, it’s probably not going to make severe symptoms go away any faster. Plus, taking two types of antihistamines can worsen their side effects and even cause ones that aren’t typical for either medication, such as drowsiness and dry mouth.
When it comes to allergy relief, talk to a healthcare provider and consider trying each antihistamine separately to see which one works better. If antihistamines aren’t enough to keep symptoms at bay, patients can also pursue other medical treatment options, such as immunotherapy and nasal sprays. All of these medicines can be purchased at a fraction of the cost with a SingleCare prescription discount card.
Sources
- Drug interactions between Allegra and Zyrtec, Drugs (2024)
- Effects of double-dose antihistamine or combined therapy in allergic rhinitis, Journal of Otorhinolaryngology, Head, and Neck Surgery (2018)
- Can I take Allegra in the morning and Zyrtec in the evening?, Drugs (2023)
- Children’s Allegra allergy 12-hour dissolve tabs, Allegra (2024)
- Comparative efficacy of cetirizine and fexofenadine for seasonal allergic rhinitis, 5-12 hours postdose, in the environmental exposure unit, Allergy and Asthma Proceedings (2005)
- Fexofenadine hydrochloride, 180 mg, exhibits equivalent efficacy to cetirizine, 10 mg, with less drowsiness in patients with moderate-to-severe seasonal allergic rhinitis, Annals of Allergy, Asthma & Immunology (2003)
