Antihistamines: what they do and how to pick the right one

Sneezing, itchy eyes, runny nose, or hives? Antihistamines are the go-to medicine for those symptoms. They block histamine, the chemical your body releases during allergic reactions. That simple action can stop itching, swelling, and sneezing fast.

Types and common uses

There are two main groups you should know about. First-generation antihistamines—like diphenhydramine (Benadryl) and chlorpheniramine—work well but often make you sleepy. They’re useful at night, for short-term allergy attacks, or for motion sickness (dimenhydrinate is a common choice for travel nausea).

Second-generation antihistamines—cetirizine (Zyrtec), loratadine (Claritin), and fexofenadine (Allegra)—cause little to no drowsiness. Use these for daily relief from hay fever, chronic rhinitis, or long-lasting hives. Some prescription options (levocetirizine, desloratadine) offer stronger or longer effects for stubborn cases.

Side effects and safety tips

Common side effects depend on the type. First-gen drugs often cause drowsiness, dry mouth, blurred vision, and urinary retention. Don’t mix them with alcohol, sleeping pills, or heavy machinery work. Second-gen drugs are kinder on alertness but can still cause headaches or mild tiredness in some people.

Certain medical conditions make antihistamines risky: narrow-angle glaucoma, enlarged prostate, severe asthma, and some heart conditions. Pregnant or breastfeeding? Some antihistamines (like loratadine and cetirizine) are commonly used, but always check with your doctor before starting anything. If you’re on multiple medications, ask about interactions—some antihistamines can boost or block other drugs.

If allergy symptoms are severe—think facial swelling, difficulty breathing, tight throat, or fainting—treat it as an emergency. Antihistamines won’t replace epinephrine in anaphylaxis. Go to the ER or call emergency services right away.

For chronic problems, like year-round allergies or persistent hives, doctors sometimes increase the dose of a second-generation antihistamine or add other treatments such as nasal steroids or montelukast. Don’t increase doses on your own without medical advice.

Practical tips: try a non-drowsy option for daytime use. Reserve diphenhydramine for short-term needs or sleep. Keep a travel-size pack of a motion-sickness antihistamine if you know you get queasy. Track what triggers your allergies and use antihistamines proactively when pollen or pet dander are likely to flare you up.

Want more on allergies during pregnancy or which antihistamines help with motion sickness? Check our related guides on pregnancy and allergies and on dimenhydrinate for practical, easy-to-follow advice.