Allergies Home > What You Need to Know About Zyrtec-D

How Does Zyrtec-D Work?

As mentioned, Zyrtec-D contains two different medications: cetirizine and pseudoephedrine. Allergies occur when the body's immune system reacts to normally harmless substances that do not bother most people. This reaction is partly caused by the release of histamine from certain cells in the body. Cetirizine is an antihistamine, which means it blocks histamine from binding to histamine receptors and causing allergy symptoms. Since histamine is responsible for many of the symptoms of allergies, blocking it can be helpful. However, antihistamines are not usually helpful for nasal congestion, which is why cetirizine is combined with pseudoephedrine.
Pseudoephedrine is a nasal decongestant. It works by constricting the blood vessels in the nose, helping to relieve nasal congestion. It is useful for relieving nasal congestion due to many causes, including allergies and the common cold.

When and How to Take It

General considerations for when and how to take Zyrtec-D include the following:
  • The medication comes in tablet form. It is taken by mouth twice a day, with about 12 hours in between doses.
  • Be sure to swallow the tablets whole. They are extended-release tablets, and will release the medication too rapidly if they are broken, chewed, or crushed.
  • You can take Zyrtec-D with or without food. If the drug bothers your stomach, try taking it with food.
  • Some people need to take Zyrtec-D all year long, while others take it only during allergy season.
  • For the medication to work properly, it must be taken as directed by the package labeling. Please read the label closely.

Dosage Information

There is only one standard recommended Zyrtec-D dosage. As is always the case, do not adjust your dose unless your healthcare provider specifically instructs you to do so.
(Click Zyrtec-D Dosing for more information.)
Written by/reviewed by:
Last reviewed by: Kristi Monson, PharmD;
Last updated/reviewed:
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