Cetirizine

For adults and children over 12, cetirizine should be taken as a once-daily dose, unless directed differently by your doctor. Tablets come as a standard 10mg dose (or 10ml of liquid).

Doses for children are determined by age group, and this is given as a liquid. They can take this twice daily. It's suitable for children over the age of two years.

During an allergic reaction your immune system releases a chemical called histamine, which is responsible for the symptoms of an allergy. Antihistamines work by opposing the actions of histamine, by stopping histamine binding to its target sites in the body.

The chemical structure of non-drowsy antihistamines makes them less likely to enter the brain through what is known as the blood-brain barrier. This makes them less likely to cause drowsiness compared to other antihistamines.

Do not take cetirizine if you have previously had an allergic reaction to cetirizine or another ingredient listed in the medication, or have reacted to an antihistamine in the past. Children under 2 years old should not take cetirizine unless prescribed by a doctor and age restrictions can vary between different cetirizine products.

Speak with your doctor or pharmacist before taking cetirizine if you are pregnant or breastfeeding, or have any of the following conditions: liver or kidney problems, epilepsy or seizures, or difficulty passing urine. You should avoid it if you are due an allergy skin test.

Cetirizine can interact with other medicines such as betahistine, certain antidepressants (called monoamine oxidase inhibitors) and dalteparin. If you take any prescription, over-the-counter or herbal medicines, ask your doctor or pharmacist to check they are safe to take alongside cetirizine.

Common side effects can include headache, dizziness, drowsiness, restlessness, dry mouth, sore throat, diarrhoea, stomach ache and feeling sick.