Cetirizine: uses, side effects and cautions

Cetirizine is an antihistamine used for hay fever, red itchy conjunctivitis, eczema, hives, reactions to bites and stings and some food allergies. It is sold as 10mg tablets and as a liquid. The NHS cautions that some Benadryl products do not contain cetirizine at all but another antihistamine such as acrivastine, so check the active ingredient on the pack.

It blocks histamine, the chemical that causes watery eyes, sneezing, a runny nose and skin rashes in allergy. Relief generally begins within an hour, a little faster than the 1 to 3 hours the NHS gives for loratadine.

Although termed non-drowsy, cetirizine seems to cause sleepiness more often than loratadine, desloratadine or fexofenadine, and much less often than sedating antihistamines such as chlorphenamine. Other non-drowsy options, including levocetirizine, seem to work as well.

The NHS gives the usual dose for adults and children aged 12 and over as 10mg once a day, with lower doses usually used if you have kidney problems. For ages 6 to 11 it is 5mg twice a day, spaced 10 to 12 hours apart, such as first thing and at bedtime. For ages 2 to 5 it is 2.5mg twice a day, and for a one-year-old the doctor uses weight or age.

Take tablets with water, milk or squash, with or without food, swallow whole and do not chew. Measure liquid with a syringe or spoon, never a kitchen teaspoon. If you buy it, follow the pack; if prescribed, follow your doctor.

If a child on twice-daily dosing misses a dose, it can be given if within 4 hours of the due time; beyond that, wait for the next dose. Some people need it for a day or two after a bite, others daily through spring and summer.

Beyond sleepiness, side effects affecting more than 1 in 100 people include headache, dry mouth, nausea, dizziness, diarrhoea and a sore throat; children are more likely than adults to get diarrhoea, sneezing or a blocked and runny nose. Dry mouth may ease with sugar-free gum. If dizzy on standing, get up slowly or sit or lie down until it passes. Severe or prolonged diarrhoea can make the contraceptive pill unreliable.

Serious side effects are rare. Easier bruising than normal, or bleeding that takes longer to stop, calls for a doctor or 111 straight away. Swelling of the lips, mouth, throat or tongue needs 999. Suspected side effects can be reported through the Yellow Card scheme.

The NHS says cetirizine is unlikely to do harm taken for a long time, but that it is best used only as long as needed. Because there is a very small chance of severe itching when treatment is stopped suddenly after regular long use, talk to your doctor before stopping if you have taken it daily for a long period.

Tell your doctor or pharmacist if you have had an allergic reaction to cetirizine or other medicines, have an allergy to food additives, have kidney failure, have epilepsy or another seizure risk, have difficulty passing urine, or are due to have an allergy test, because cetirizine may affect the result and you may need to stop it a few days earlier.

The NHS names no specific interacting drugs, but asks you to check about anything that causes drowsiness, dry mouth or difficulty passing urine, since cetirizine may add to those effects. Paracetamol and ibuprofen can be taken with it, and so can steroid nasal sprays and eye drops. Alcohol is best avoided, as it can add to sleepiness.

Cetirizine can be taken in pregnancy; information is limited but nothing suggests harm to the baby. If you need an antihistamine while breastfeeding, the NHS describes cetirizine as one of the best choices. Tell a health professional or call 111 if your baby feeds poorly or seems unusually sleepy or irritable.

An extra dose is unlikely to harm an adult. Call 111 if your child takes more than the recommended dose even without symptoms, or if you are worried or have a headache, sleepiness or a fast heartbeat.