What should you know about OTC oral antihistamines?

These medicines reduce the effects of histamine, a chemical released during some allergic reactions. They may calm sneezing, a runny nose, itchy eyes, and an itchy throat. They are commonly used for allergic rhinitis, allergic conjunctivitis, and reactions to triggers such as pets or house dust mites.

Some older antihistamines can make you sleepy, slow your reactions, or leave you with a dry mouth. Newer options are often less sedating, but drowsiness can still occur. An oral antihistamine may help allergy-related nasal symptoms while being less useful for a severely blocked nose than a treatment designed specifically for congestion.

Read the package directions and use only the stated dose. Check the active ingredients before combining a cold remedy, sleep aid, or another allergy product, because more than one product may contain an antihistamine. Do not drive, cycle in traffic, or operate machinery until you know how the medicine affects you, and avoid alcohol if it increases sleepiness.

Ask a pharmacist or clinician before use if you are pregnant or breastfeeding, have glaucoma, difficulty passing urine, liver or kidney disease, or take regular medicines. Children need an age-appropriate product and dose. If symptoms keep returning, treatment is needed often, or the medicine is not helping, arrange a review rather than repeatedly changing products.

Get emergency help immediately for trouble breathing, swelling of the lips, tongue, or throat, faintness, or rapidly worsening symptoms after an exposure. An antihistamine is not a substitute for emergency treatment of a severe allergic reaction.

Seek medical advice for a new or severe reaction, symptoms involving the eyes with pain or vision changes, fever or facial pain with nasal symptoms, or a rash that is widespread, blistering, or affecting the mouth. A clinician can check whether the symptoms are allergy-related and whether another treatment is more suitable.

Which symptom should this medicine target, and when should I take it? Could it make me drowsy or interact with my regular medicines? Would a nasal spray, eye drop, or trigger-avoidance plan fit my symptoms better?