What is Cetirizine and how does it work?

Cetirizine is a non-sedating antihistamine used to treat allergies and chronic idiopathic urticaria. 

This medicine works by preventing the actions of histamine. Histamine acts on histamine receptors which causes a chain reaction that results in allergies symptoms. Histamine is a substance produced by the body when it reacts to a foreign substance such as pet fur or pollen. Cetirizine blocks histamine receptors and so stops the chain reaction that causes the symptoms of the allergy. It usually starts to work within half an hour to an hour after taking a dose. 


This occurs when your immune system reacts to a foreign substance. Your immune system makes substances known as antibodies. When you have allergies, your immune system makes antibodies that identify a particular allergen as harmful even though it isn’t. The severity of allergies varies from person to person. While most allergies can’t be cured, treatments can help relieve your allergy symptoms. Allergy symptoms can affect your airways, nasal passages, or sinuses. Allergic reactions can range from mild to severe. In most severe cases, allergies can trigger a life-threatening reaction known as anaphylaxis.

An allergy starts when your immune system mistakes a normally harmless substance for a dangerous invader. The immune system then produces antibodies that remain on the alert for that particular allergen. When you’re exposed to the allergen again, these antibodies can release several immune system chemicals. 

Chronic idiopathic urticaria 

These are red and itchy welts that result from a skin reaction. The welts vary in size and appear and fade repeatedly as the reaction runs its course. The condition is considered chronic hives if the welts appear for more than 6 weeks and recur frequently over months or years. This condition may be uncomfortable and interfere with sleep and daily activities. The signs and symptoms may include:

  • Welts that vary in size, change shape and appear/fade repeatedly
  • Batches of red or skin-colored welts
  • Itching which may be severe
  • A tendency of signs and symptoms to flare with triggers  
  • Painful swelling of the lips, eyelids, and inside the throat
  • A tendency for signs and symptoms to persists for more than six weeks 

The welts that come with hives arise when certain cells release histamine and other chemicals into your bloodstream. Doctors often can’t identify the reason for chronic hives or why acute hives sometimes turn into a long-term problem. The skin reaction may be triggered by:

  • Pain medications
  • Infection
  • Insects or parasites
  • Scratching
  • Stress
  • Heat or cold
  • Sunlight
  • Alcohol or food
  • Exercise
  • Pressure on the skin as from a tight waistband

In most cases, this condition may be related to an underlying illness. 

Chronic idiopathic urticaria doesn’t put you at any sudden risk of a serious allergic reaction. But, if you do experience hives as part of a serious allergic reaction, seek medical help. 

How to use Cetirizine?

Cetirizine is taken usually once a day. Each dose may either be taken with or without food. The medicine is taken by mouth with a full glass of water. Swallow the drug as a whole without crushing or chewing it. Drink plenty of fluids unless otherwise directed by your doctor. Take Cetirizine exactly as it is given by your doctor. Do not take more or less than it is prescribed. Stop taking Cetirizine and call your doctor if your condition does not improve during the first 3 days of your treatment or if your condition lasts longer than 6 weeks. 

The dosage is based on your medical condition and response to the treatment. Do not increase your dose without any consent from your doctor. If your doctor directs you to take this medication daily, take it regularly to get the most benefit from it. To help you remember, take it at the same time and in the same way each day. 

What are the side effects of Cetirizine?

Common side effects:

  • Fatigue
  • Drowsiness
  • Dizziness
  • Tired feeling
  • Sore throat
  • Dry mouth
  • Nausea
  • Cough
  • Headache
  • Constipation 
  • Stomach pain
  • Vomiting 

Stop taking this medicine and call your doctor right away if these occur:

  • Little or no urination
  • Problems with vision
  • Confusion
  • Severe restless feeling
  • Hyperactivity
  • Weakness
  • Tremors
  • Sleep problems or insomnia 
  • Fast pounding, or uneven heartbeat 


  • Cetirizine can be taken by adults and children aged two years and over.
  • Cetirizine is not recommended for use in children under two years of age. Always check the age limit on the product you’re using. Some forms shouldn’t be given to children below a certain age. 
  • A person with kidney problems and who suffer from epilepsy need to lower their dose or extra monitoring when taking this drug.
  • Cetirizine is called a non-sedating or non-drowsy antihistamine because it doesn’t enter the brain in significant amounts. For this reason, it’s unlikely to cause drowsiness. However, some people do find that it makes them feel slightly drowsy. Make sure you know how you or your child reacts to it before doing potentially hazardous activities like cycling, driving, operating machinery.
  • It is fine to drink alcohol with cetirizine.
  • If you’re due to have any skin prick or patch test to diagnose allergies, you should stop taking Cetirizine at least three days before the tests. This is because antihistamines can prevent or lessen the skin reactions that indicate an allergy and so can make the test results unreliable.
  • There is no evidence that Cetirizine is harmful if used during pregnancy. If you suffer from allergies during pregnancy you should get advice from your doctor on how to treat your symptoms. Some locally acting medicines like nasal sprays or creams are usually preferred. If you need an antihistamine while pregnant cetirizine can be used, but only if the benefits outweigh any risks and only if it’s prescribed by your doctor. Your doctor can give you more information.
  • It is fine to take painkillers such as paracetamol, ibuprofen, and co-codamol with Cetirizine.
  • Keep your medicine away from light, heat, and reach of children. Store it at room temperature and throw away any drug that has passed the expiration date.