Cetirizine belongs to the class of medications called second-generation antihistamines, specifically the class known as histamine receptor antagonists. For adults and children 2 years of age and older, it is used for the relief of symptoms associated with seasonal allergies including sneezing; itchy nose and throat; stuffy and runny nose; and tearing, red, or itchy eyes. It is also used for the relief of symptoms associated with allergic skin conditions (e.g., chronic idiopathic urticaria) such as itchy skin and hives. For adults and children over the age of 12 years, it is also used for the relief of symptoms associated with year-round allergies and hives.

Cetirizine works by blocking the actions of one of the body's natural chemicals known as histamine. Histamine is responsible for many of the symptoms caused by allergies.

Cetirizine usually starts to relieve allergy symptoms within 20 minutes and lasts for 24 hours.

This medication may be available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of this medication may not be used for all of the conditions discussed here.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

The recommended dose for adults and children 12 years of age and older is 5 mg to 10 mg once daily taken by mouth depending on the severity of the symptoms and circumstances of the person taking the medication. If 10 mg once daily is not enough to control your allergy symptoms, talk to your doctor.

For adults 65 years of age and over, the recommended dose is 5 mg once daily.

For children 6 to 12 years of age, the recommended dose is 10 mg once daily or 5 mg in the morning and in the evening.

For children 2 to 6 years of age, the recommended dose is 5 mg (one teaspoon) given once daily, or 2.5 mg (one-half teaspoon) of syrup in the morning and evening.

Use an oral syringe to measure each dose of the liquid, as it gives a more accurate measurement than household teaspoons.

All forms of cetirizine may be taken with or without food.

Seniors, and people with kidney or liver problems, may need lower doses of this medication.

Children should not use this medication for more than 14 days at a time unless recommended by a doctor.

Many things can affect the dose of medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones listed here, do not change the way that you are taking the medication without consulting your doctor.

It is important to take this medication exactly as suggested by your doctor or pharmacist. If you miss a dose, take it as soon as possible and continue with your regular schedule. If it is almost time for your next dose, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

Store this medication at room temperature, protect it from moisture, and keep it out of the reach of children.

Do not take this medication if you:

• are allergic to cetirizine or any ingredients of the medication
• are allergic to hydroxyzine
• have severely reduced kidney function

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

• decreased sexual ability
• dizziness
• dry mouth
• headache
• loss of taste
• sleepiness
• trouble sleeping

Although most of the side effects listed below don't happen very often, they could lead to serious problems if you do not seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

• eye pain or swelling
• behaviour changes (e.g., agitation, aggression)
• blurred vision
• difficult or painful urination
• forgetfulness
• hallucination (hearing or seeing things that aren't there)
• new rash or itching after stopping the medication
• restlessness with increased body movement
• signs of liver problems (e.g., nausea, vomiting, diarrhea, loss of appetite, weight loss, yellowing of the skin or whites of the eyes, dark urine, pale stools)

Stop taking the medication and seek immediate medical attention if any of the following occur:

• signs of a serious allergic reaction (e.g., abdominal cramps, difficulty breathing, nausea and vomiting, or swelling of the face and throat)
• signs of a severe skin reaction such as blistering, peeling, a rash covering a large area of the body, a rash that spreads quickly, or a rash combined with fever or discomfort

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Before you begin using a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication.

Drowsiness/reduced alertness: Studies have shown that cetirizine does not cause drowsiness under normal circumstances. A small percentage of people taking this medication have experienced a degree of drowsiness. Do not drive or operate machinery if you become drowsy while taking this medication.

Reduced kidney function: If you have reduced kidney function, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Reduced liver function: If you have reduced liver function, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Pregnancy: This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately.

Breast-feeding: It is not known if cetirizine passes into breast milk. If you are breast-feeding and taking this medication, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: The safety and effectiveness of using this medication for seasonal allergies and allergic skin conditions have not been established for children less than 2 years of age. The safety and effectiveness of using this medication for year-round allergies have not been established for children 12 years of age and under.

Seniors: Seniors may be more sensitive to the effects of cetirizine. Therefore, a lower starting dose may be recommended by your doctor or pharmacist.

There may be an interaction between cetirizine and any of the following:

• acetylcholinesterase inhibitors (e.g., donepezil, galantamine, rivastigmine)
• aclidinium
• alcohol
• amantadine
• amphetamines (e.g., dextroamphetamine, lisdexamfetamine)
• other antihistamines (e.g., azelastine, diphenhydramine, chlorpheniramine, hydroxyzine, rupatadine)
• antipsychotics (e.g., cariprazine, chlorpromazine, clozapine, haloperidol, olanzapine, quetiapine, risperidone)
• atropine
• barbiturates (e.g., butalbital, phenobarbital)
• benzodiazepines (e.g., alprazolam, lorazepam, diazepam)
• benztropine
• botulinum toxin
• brimonidine
• buprenorphine
• cannabis
• chloral hydrate
• clidinium
• clonidine
• darifenacin
• dimenhydrinate
• diphenoxylate
• disopyramide
• domperidone
• efavirenz
• entacapone
• esketamine
• ethopropazine
• fesoterodine
• flibanserin
• flunarizine
• glucagon
• glycopyrrolate
• glycopyrronium
• ipratropium
• kava kava
• ketamine
• lemborexant
• methadone
• metoclopramide
• mirabegron
• mirtazapine
• monoamine oxidase inhibitors (e.g., moclobemide, phenelzine, tranylcypromine)
• muscle relaxants (e.g., baclofen, cyclobenzaprine, methocarbamol, orphenadrine)
• nabilone
• narcotic pain medications (e.g., codeine, fentanyl, oxycodone, morphine, tapentadol, tramadol)
• nitroglycerin
• olopatadine
• oxybutynin
• perampanel
• pitolisant
• pizotifen
• pomalidomide
• potassium supplements (potassium chloride, potassium citrate)
• pramipexole
• pregabalin
• prucalopride
• ropinirole
• rotigotine
• seizure medications (e.g., clobazam, levetiracetam, phenobarbital, phenytoin, primidone, rufinamide, topiramate, valproic acid)
• sodium oxybate
• solifenacin
• tetrabenazine
• thiazide diuretics (water pills; e.g., hydrochlorothiazide, indapamide, metolazone)
• tiotropium
• tizanidine
• tolterodine
• trazodone
• tricyclic antidepressants (e.g., amitriptyline, clomipramine, desipramine, trimipramine)
• trospium
• umeclidinium
• valerian
• zolpidem
• zopiclone

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.