Examples of antihistamines and how they differ

The active ingredient matters more than the brand name. Products may be tablets, liquids, eye drops, nasal preparations or skin treatments, and a familiar brand can contain different ingredients in different formulations.

Cetirizine, loratadine and fexofenadine are commonly described as less-sedating oral antihistamines, although sleepiness can still occur. Chlorphenamine and diphenhydramine are sedating examples and can impair alertness, coordination and reaction time. Antihistamine eye drops may target allergic eye symptoms with less whole-body exposure.

Antihistamines can relieve histamine-related sneezing, itching, hives and a runny nose. They are less helpful for nasal blockage when swelling is the dominant problem, and they do not treat every cause of a rash, itch or cold symptom.

Match the formulation to the symptom and use the dose on the product label or prescription. Check the active ingredient before combining an allergy tablet with a cold, flu, travel-sickness or sleep remedy; two products may contain medicines from the same sedating group.

Ask a pharmacist to check suitability for a child, an older adult, pregnancy or breastfeeding, kidney or liver problems, glaucoma, difficulty urinating, or regular use of sedatives. If drowsiness occurs, do not drive, operate machinery or mix the medicine with alcohol.

Call emergency services for difficulty breathing, faintness, or swelling of the tongue or throat. Antihistamines are not a substitute for emergency treatment of a severe allergic reaction.

Seek clinical advice if symptoms do not respond as expected, repeatedly return, affect sleep, or require frequent medicine. Severe confusion, unusual agitation, trouble passing urine or a fast irregular heartbeat after a dose also needs prompt medical advice.

Ask which ingredient fits the symptom location, whether daytime alertness changes the choice, and whether a local preparation could be appropriate. Give the clinician a complete list of prescriptions, supplements and non-prescription remedies.