Cetirizine

• The usual dose of cetirizine for adults, and children 12 years of age or over, is 1 tablet (10 milligrams) once a day.
• The dose for children under 12 years will depend on their age and weight. Your healthcare provider or pharmacist will advise you on the correct dose for your child.
• You can just take cetirizine on the days you need it. It can be restarted if the symptoms come back. 
• Some people take cetirizine for a few weeks when their allergies are a problem, such as in spring. Others take it long-term to help control allergy symptoms. 

• Timing: Take cetirizine once a day at the same time each day. 
• Food: You can take cetirizine with or without food.
• Capsules or tablets: Swallow the tablet whole, with a glass of water.
• Liquid cetirizine: Shake the bottle well and use an oral syringe or measuring spoon to measure each dose.
• Missed dose: It isn't harmful if you miss your cetirizine dose. If you forget to take your dose, and you usually take it regularly, take it as soon as you remember that day. If it's less than 12 hours for your next dose, just take the next dose at the usual time. Don't take double the dose.

• Are you pregnant, trying for a baby or breastfeeding?
• Do you have epilepsy?
• Do you have any problems with the way your kidneys work?
• Are you taking or using any other medicines? This includes any medicines that you can buy without a prescription, as well as herbal and complementary medicines.

If so, it’s important that you tell your healthcare provider or pharmacist before you start cetirizine.

Sometimes a medicine isn’t suitable for a person with certain conditions, or it can only be used with extra care.

Here are some things to know when you're taking cetirizine. Other things may be important as well, so ask your healthcare provider what you should know about.

• Alcohol: Limit drinking alcohol while you’re taking cetirizine. It may increase your chance of side effects such as feeling sleepy.  
• Driving: Some people might feel sleepy when taking cetirizine. Be careful when driving or using tools until you know how this medicine affects you.
• Other medicines: Cetirizine may interact with some medicines so check with your pharmacist before starting cetirizine or before starting any new medicines. If you take it with other antihistamines, such as some cough and cold medicines, it may make you even more sleepy.

Like all medicines, cetirizine can cause side effects, although not everyone gets them. If you're concerned about any symptoms you think might be related to your medicine, talk to your healthcare provider. The following information offers some guidance but doesn't include all possible side effects.

Common side effects

Tell your healthcare provider if these side effects bother you.

• Mild headache: Drink plenty of water.
• Feeling tired or sleepy: This can happen if you take too much cetirizine or you’re sensitive to the medicine. Try taking cetirizine at night. Be careful when driving or using tools until you know how this medicine affects you. Avoid or limit alcohol – it makes these symptoms worse.

Tell your healthcare provider immediately or phone Healthline free on 0800 611 116 if these occur

• Changes in eyesight.
• Dry mouth.
• Feeling dizzy or confused.
• Problems passing urine (peeing).
• Constipation (hard poo).

Phone 111 for an ambulance or go to your nearest accident and emergency (A&E) clinic if these occur

• Signs of an allergic reaction such as itchy skin, and rash, swollen lips or tongue, problems breathing, like a tight chest or shortness of breath.

Read more about medicines and side effects and reporting a reaction you think might be a side effect.