Antihistamine: how they work and which one to pick

Got sniffles, itchy eyes, or hives? Antihistamines are the first thing many people reach for. They block histamine, a chemical your body releases during an allergic reaction. That simple action eases sneezing, runny nose, itching, and watery eyes fast.

Not all antihistamines act the same. You’ll hear terms like first-generation and second-generation. First-generation drugs (diphenhydramine, chlorpheniramine) work well but often make you sleepy. Second-generation options (loratadine, cetirizine, fexofenadine) usually cause less drowsiness and last longer—good for daily use during allergy season.

How antihistamines work and what they treat

Histamine attaches to receptors in your nose, skin, and eyes and causes allergy symptoms. Antihistamines block those receptors. That reduces swelling and itch. They help with seasonal allergies, indoor allergies, and chronic hives. Some types also ease motion sickness or sleep problems, but you should only use them for those reasons when a doctor recommends it.

For nasal congestion, antihistamines alone may not be enough. An intranasal steroid spray or a decongestant can help—but check with your pharmacist or doctor before combining medicines.

Choosing the right antihistamine and staying safe

Want non-drowsy relief? Try loratadine or fexofenadine. Need faster relief or short-term sleep help? Diphenhydramine works but plan to rest—don’t drive after taking it. If you have chronic allergies, a daily second-generation tablet is often better than taking a sedating pill only when symptoms flare.

Watch for side effects: dry mouth, dizziness, blurred vision, constipation, and trouble peeing. Older adults are more sensitive to these effects and should avoid first-generation antihistamines when possible. Pregnant or breastfeeding? Check with your healthcare provider—some antihistamines are safer than others.

Mixing meds can be risky. Don’t combine two different oral antihistamines without advice. Avoid alcohol and other sedatives if your antihistamine causes drowsiness. If you’re taking heart or high blood pressure drugs, ask a pharmacist about interactions.

If allergy pills don’t control symptoms, consider other options: nasal steroid sprays, eye drops, allergy shots (immunotherapy), or talking to an allergist. Emergency signs—tight throat, trouble breathing, lightheadedness, or swelling of the face—need immediate medical help.

Short practical tips: read the label, follow dosing instructions, try a non-drowsy option for daytime, and keep a sedating antihistamine for bad nights only. If you shop online, use reputable pharmacies and keep records of prescriptions. Want help picking a brand or comparing options? Our articles on antihistamine alternatives and common allergy meds can guide you to sensible choices.