The FDA Just Discovered A New Uncomfortable Side Effect For This Popular Allergy Med

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18-06-2025

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Allergy season is in full swing, and chances are, if you're one of the 25 percent of adults who suffer from seasonal sniffles, you're reaching for your trusty meds. Zyrtec is a super popular over-the-counter option because it's pretty darn reliable to treat your symptoms. But, as with any other drug, it's important to keep Zyrtec side effects in mind so you can get all the benefits while minimizing any potential downsides.
Zyrtec is an antihistamine and it blocks histamines to stop allergic reactions, says Virginia Boomershine, an ambulatory clinical pharmacy regional senior manager for Banner Pharmacy Services. Histamines are the culprits behind all those pesky allergy symptoms, like itchy, watery eyes, runny nose, scratchy throat, and sneezing.
The good news is there are fewer side effects from Zyrtec compared to first-generation antihistamines such as Benadryl (which you actually shouldn't be taking at all), and it's relatively safe even at higher than standard doses for most people, says Jennifer Toh, MD, an allergist and immunologist at ENT and Allergy Associates.
Below, docs share *all* the possible side effects you might experience on the med. Take note: most of the entries below include the word "rare." That's because side effects on Zyrtec are uncommon. Any side effects are typically mild, and a majority of people can take the medication with no issues, adds Purvi Parikh, MD, an allergist and immunologist at Allergy & Asthma Network. Keep reading to find out whether this medication is right for you and what you can do about the potential side effects.
Meet the experts: Jennifer Toh, MD, is an allergist and immunologist at ENT and Allergy Associates. Purvi Parikh, MD, is an allergist and immunologist at Allergy & Asthma Network. Virginia Boomershine is an ambulatory clinical pharmacy regional senior manager for Banner Pharmacy Services. Maria Shtessel, MD, is an assistant professor of medicine, division of clinical immunology at Mount Sinai. Robert Eitches, MD, is an allergist at Tower Allergy.
It's best to be aware of potential Zyrtec side effects—especially if you're planning on popping the stuff on the reg over the next few months.If you've ever slept 14 hours after popping a Benadryl, you're well aware that some allergy meds can seriously knock you out. That's not as common with Zyrtec, but 11 to 14 percent of people do report feeling sleepy after taking it, making it the most common side effect reported, says Boomershine.
Since the effects of Zyrtec last 24 hours, drowsiness can hit at any time. Avoid alcohol and be careful about driving if the med hits you with the sleepies, per the Zyrtec site.When you have an allergic response, your tissue secretes more fluid (hello runny nose and watery eyes). Antihistamines, therefore, dry you up, which means that dry mouth is a possibility—but only a small one. Less than 10 percent of Zyrtec poppers will wind up with dry mouth, says Boomershine.
Drinking water will help, she says, as will switching to an alcohol-free mouthwash, as that ingredient also dries you out.Dizziness can be a rare potential side effect and may disappear after your body adjusts to the medication, per the Mayo Clinic. Give it time, but always check in with your doctor if you're concerned. And, just like with drowsiness, hold off on driving if you're feeling wobbly.Zyrtec may cause insomnia because the medicine can block acetylcholine, an important neurotransmitter, says Dr. Parikh. Acetylcholine is involved in the initiation of REM sleep (i.e., the sleep stage most commonly associated with dreaming), so if those neurons are inhibited, you may have trouble falling and staying asleep. Luckily, this side effect is rare.
It can also turn kids into little insomniacs, says Boomershine. Having them take the long-acting med earlier in the day won't help either since it lasts all day. Talk to their pediatrician about making a switch.It's incredibly rare, according to the National Institutes of Health, but keep it on your radar anyway. While you may be taking Zyrtec to prevent allergy symptoms, it's possible to have a potentially deadly allergic reaction called anaphylaxis from the medication itself. (FYI: This is a risk with all medications, not just Zyrtec.) If you develop hives, swelling, shortness of breath, wheezing, and chest tightness, call 911 immediately.
(Psst: Looking for the best allergy med, according to allergy doctors? Get their verdict here.)If you experience a sore throat while taking Zyrtec, it's likely because your mucous membranes, the inner lining of your body and organs, become drier, causing the tissue in your mouth to also feel more parched and lead to a sore throat, says Dr. Eitches. And coughing can be an instinctive response to try to moisten the mouth.
To combat this, stay hydrated. But if this side effect becomes too severe, Dr. Eitches suggests switching to a different antihistamine.Constipation is a very rare side effect that happens due to a drug's anticholinergic effect, which means the drug blocks neurotransmitters that affect how the body functions. In this case, certain receptors that help gut motility are blocked. This side effect was much more common with older, first-generation antihistamines such as Benadryl, says Dr. Patel.
It's not as common with Zyrtec, but if this does happen to you, Dr. Eitches recommends trying a different antihistamine, adding fiber to your diet, and staying well-hydrated to get things moving again.Anxiety is another super rare side effect of Zyrtec, but it is possible, says Dr. Parikh. Remember acetylcholine? Turns out blocking it may also trigger anxiety and fast heart rate because acetylcholine regulates heart contractions and blood pressure as well.
You should stop feeling antsy once you discontinue the medication, but if quitting it is not an option, talk with your doctor about other drugs that can help you manage your allergies, notes Dr. Parikh.As of May 2025, the FDA issued an alert that discontinuing Zyrtec after long-term use may result in severe pruritus (or, itchiness) within a few days. It's rare, but can sometimes require medical intervention.
"I always counsel my patients who have been on Zyrtec for long periods of time to taper the medication off slowly," says Maria Shtessel, MD, an allergist and immunologist at Mount Sinai. "For example, [they can start by] taking it first every other day, and increasing the days between doses slowly before completely stopping."Yep. "When taken in the recommended doses, antihistamines can be taken daily. This is especially true with Zyrtec, since it doesn't show decreasing effectiveness if used daily," says Sima Patel, MD, an allergist at New York Allergy & Sinus Centers.
Still, it's probably worth holding off on medication that you don't need, says Dr. Patel. So if you aren't having allergy symptoms or they get milder during a certain time of the year, that's probably a good time to take a Zyrtec break. "We always want the least amount of medication to control symptoms. However, starting allergy medications two weeks prior to your symptomatic season is best to help prevent symptoms," Dr. Patel says.It depends on whether you experience any side effects, says Robert Eitches, MD, an allergist at Tower Allergy. If your problems are only during the day time and you aren't really prone to side effects, then go ahead and take it during the day.
But if you experience side effects like drowsiness, Dr. Eitches recommends taking your dose at night before bed. "That way you wake up in the morning relatively clearer too," he says. If it makes you sleepy, the side effect will have likely worn off by the time you wake up, and since the medication can provide relief for 24 hours, you'll still experience relief during the day.Zyrtec is safe for most people, but there are some individuals who should stay away. Children under 2, anyone with a history of an allergic reaction to Zyrtec or hydroxyzine/piperazine derivatives, and those with severe renal impairment shouldn't take Zyrtec, says Dr. Patel. If you are pregnant and breastfeeding, Dr. Patel recommends speaking to your doctor before using it.
The medication is "primarily eliminated from your body through the kidneys," says Dr. Parikh. So, if your kidneys aren't functioning properly, the medication can accumulate and build up in your blood, which may cause additional damage to your kidneys and severe side effects.
Additionally, if you take any medications that can cause sedation, such as benzodiazepines, you should talk with your doctor before taking Zyrtec, says Dr. Parikh, because combining the two may cause worsened side effects. Other antihistamines are typically okay to take with Zyrtec as long as they don't make you too sleepy, she adds. And it's always a good idea avoid alcohol when you're on Zyrtec.
When in doubt, go to your doctor with any questions before you take Zyrtec to quell allergy symptoms.
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