Cetirizine is an allergy medication that you can buy over the counter (OTC) at a pharmacy. That is, you don’t need a prescription.

Cetirizine comes in capsules and tablets. You typically take it just once per day, and it begins to work quickly.

It’s inexpensive, too­ — usually less than $1 per day for brand-name versions (Zyrtec, Aller-Tec, and Alleroff), and even less for generic products.

Generally, cetirizine is a safe and effective drug, but you should be aware of certain warnings and precautions when taking this drug. Learn how this drug works, what it’s used for, and how to take it safely.

If you have year-round allergies, or seasonal allergies like hay fever, your doctor may recommend cetirizine. Cetirizine may help relieve allergy symptoms, but it doesn’t prevent them.

When you come in contact with substances that you may be allergic to (allergens), your body produces a chemical called histamine. Histamine causes most of the symptoms related to allergic reactions.

Cetirizine is an antihistamine. It blocks the effects of histamine.

Cetirizine helps relieve mild to moderate allergy symptoms, such as:

  • sneezing
  • runny nose
  • itchy or watery eyes
  • itchy throat or nose

These reactions can happen after you touch or inhale allergens such as plant pollen, mold, or pet dander. Allergies usually affect your nose, sinuses, throat, and other areas of your upper respiratory system.

Cetirizine also helps relieve hives. Hives are itchy, raised rashes on the skin. They often occur with food or medication allergies.

Adults and children 6 years and older can take cetirizine capsules and tablets.

The usual dosage for adults younger than 65 years and children who are 6 years and older is one 10-milligram (mg) dose per day.

You shouldn’t take more than 10 mg in 24 hours. Your doctor may recommend a 5-mg dose once or twice per day if your allergies are mild.

Talk to your doctor about dosage for people who:

  • are 2 to 6 years old
  • are older than 65 years
  • have liver or kidney disease

Cetirizine is a newer, second-generation antihistamine. Unlike first-generation antihistamines, cetirizine is less likely to cause side effects such as dangerous drowsiness, dry mouth, blurred vision, and overheating.

That said, Cetirizine can cause adverse effects, such as:

  • some drowsiness
  • excessive tiredness
  • dry mouth
  • stomach pain
  • diarrhea
  • vomiting

Tell your doctor about any unexpected side effects that you have while taking cetirizine. Also, discuss any ongoing or bothersome side effects. These side effects are usually not emergencies.

Following are a few things to consider before taking cetirizine.

Be careful using machinery

Even though cetirizine doesn’t usually cause drowsiness, some people respond differently when taking it, especially in the first few doses.

Be cautious. Don’t drive your car or use machinery until you know for sure how your body will respond to cetirizine.

Check the ingredients

Don’t use cetirizine if you have ever had an allergic reaction to it or to any of the ingredients in it. Also, steer clear of cetirizine if you’re allergic to any antihistamine that contains hydroxyzine.

Use caution if you’re pregnant or breastfeeding

Talk to your doctor or healthcare provider before you take cetirizine if you are pregnant or planning to become pregnant, or if you’re breastfeeding. Taking cetirizine is generally safe during pregnancy.

Talk to your doctor if you have certain conditions

If you have liver or kidney disease, ask your doctor about taking cetirizine. If your doctor feels it’s safe for you to take, they may recommend taking less than the typical dosage.

Cetirizine does interact with other substances.

For example, avoid consuming alcoholic drinks while you take cetirizine. Doing so may be dangerous. Mixing cetirizine with alcohol can cause drowsiness or make you less alert.

If you take any type of tranquilizer, sedative, or sleep aid, make sure to mention this to your doctor before you use cetirizine.

Mixing cetirizine with drugs that depress your central nervous system can increase sleepiness. It can also further affect your mental and nervous system functions.

There is a possibility of a drug interaction between cetirizine and theophylline. Theophylline (Theo-24) is a drug that some people with asthma and other lung problems take.

In some instances when the two drugs were taken, it took longer for cetirizine to leave the body. However, the interaction may be dose-related. It has only been reported with daily theophylline doses of 400 mg or more.

Talk to your doctor if you take theophylline and are considering cetirizine.

Cetirizine-D and brand-name versions, such as Zyrtec-D, are combination drugs. The “D” stands for decongestant. These drugs contain both cetirizine and the decongestant pseudoephedrine.

Pseudoephedrine is a stimulant and can make certain health conditions worse. Your doctor may tell you that cetirizine-D is not for you if you have any of these conditions:

  • heart disease
  • thyroid disease
  • diabetes
  • glaucoma
  • high blood pressure
  • enlarged prostate with urinary retention

Cetirizine is an OTC drug that can relieve mild to moderate allergy symptoms. Like any drug, especially OTC medication, you should understand all of the considerations before you start taking it.

Talk to your doctor about any questions you have about your symptoms and any other conditions you may have. Your doctor may recommend a different antihistamine or a combination drug of cetirizine and another product that may require a prescription.

Here are a few questions you might ask your doctor about cetirizine:

  • Is cetirizine a good choice for me? What are my options and alternatives?
  • How often should I take cetirizine, and how much should I take?
  • What effects will I notice after I take cetirizine?
  • Can I take cetirizine with my other medications and health conditions?
  • Are there any other dangers or risks associated with this medication?
  • What are the signs of an emergency, and what should I do in case of an emergency?

Cetirizine tablets

In addition to capsules, cetirizine comes in tablets that you can swallow, chew, or let dissolve in your mouth.

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