Expired Allergy Medicine: What Happens When You Take It?

When you find an old bottle of expired allergy medicine, a medication designed to block histamine and reduce symptoms like sneezing, itching, and runny nose. Also known as antihistamines, these pills include common brands like Claritin, Zyrtec, and Benadryl. They’re meant to give you relief when pollen, dust, or pet dander hit hard—but what if the expiration date passed months or years ago? Most people assume expired meds are just useless. But some people take them anyway, thinking, "It’s just an allergy pill, how bad could it be?" The truth is more complicated.

Antihistamines, a class of drugs that block histamine receptors to calm allergic reactions. Also known as allergy pills, they’re among the most commonly stored over-the-counter medications in homes. But like all drugs, they degrade over time. Moisture, heat, and light break down the active ingredients. A 2012 FDA study found that 90% of expired drugs were still potent—*if stored properly*. But that doesn’t mean yours is safe. If you kept your Zyrtec in a humid bathroom, or left your Benadryl in a hot car, the chemical structure may have changed. That doesn’t just mean it won’t work—it could cause unexpected side effects.

Drug expiration, the date after which a manufacturer can no longer guarantee full potency or safety. Also known as medication safety, this isn’t just a marketing tactic. It’s based on real stability testing. Manufacturers test pills under controlled conditions to see how long they hold up. But real life? Your medicine cabinet isn’t a lab. If you’re taking expired allergy medicine during peak allergy season and your symptoms aren’t improving, you’re not being lazy—you might be getting a weaker dose. Worse, if you’re relying on it to prevent anaphylaxis, a failed pill could be dangerous.

Some antihistamines break down into harmless compounds. Others? Not so much. Old liquid forms can grow bacteria. Tablets might crumble or stick together. And if you’re using nasal sprays past their expiration, the pump mechanism can fail, leading to uneven dosing. The FDA doesn’t require drugmakers to prove safety after expiration—but that doesn’t mean it’s safe. It just means the burden is on you to decide.

Here’s what you should do: Check the expiration date. If it’s passed, don’t take it if you’re treating a serious allergy. If it’s just seasonal sneezing, and the pills look dry, intact, and smell normal, you *might* be okay—but don’t count on full strength. Better yet, replace it. Most antihistamines are cheap, and your comfort isn’t worth the risk. And if you’ve got a drawer full of old meds? Don’t flush them. Don’t toss them in the trash. Find a take-back program or pharmacy drop-off. Your water supply and local wildlife will thank you.

Below, you’ll find real stories and science-backed advice on what happens when meds go bad, how to store them right, and when to throw them away—without wasting money or risking your health.