Cetirizine is an allergy medication that you can buy over-the-counter at a pharmacy. That is, you don’t need a prescription. The medication comes in capsules, tablets, and a syrup. 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 symptoms, or seasonal allergies like hay fever, your doctor may recommend cetirizine. Cetirizine may help relieve these allergy symptoms, but it doesn’t prevent them.

When you come in contact with 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. They are itchy, raised rashes on the skin. Hives often occur with food or medication allergies.

Adults and children 2 years and older can take the syrup, which is fruit flavored. Adults and children 6 years and older and take the capsules and tablets.

The usual dosage for adults younger than 65 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:

  • 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 effects are usually not emergencies.

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, and 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 are allergic to any antihistamine that contains hydroxyzine.

Don’t use during pregnancy and breastfeeding

Talk to your doctor before you take cetirizine if you are pregnant or planning to become pregnant. Taking cetirizine is generally not recommended during pregnancy. It’s also not recommended if you breastfeed your child. This is because the drug passes into breast milk.

Talk to your doctor

If you have liver or kidney disease, ask your doctor about taking cetirizine. If your doctor feels it is 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 ask your doctor before you use cetirizine. Mixing cetirizine with drugs that depress your central nervous system can amplify sedation. It can further impair your mental and nervous system functions.

There is a possibility of a drug interaction between cetirizine and theophylline. Theophylline (Theo-24, Theolair) is a drug that some people with asthma and other lung problems take. However, the interaction is most likely dose-related. It has only been reported with daily theophylline doses of 400 mg or more. In these cases, it took longer for cetirizine to leave the body. 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.

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 over-the-counter drug that can relieve mild to moderate allergy symptoms. Like any drug, especially over-the-counter 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. It 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?