Zyrtec (cetirizine hydrochloride)

For Allergy Relief

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Zyrtec, or cetirizine hydrochloride (HCl), is a “second-generation” antihistamine, available over-the-counter, which is used to treat your symptoms of allergies such as sneezing, rhinitis (runny nose), coughing, itchy eyes, itchy nose, and mild hives.

The chief advantage of the second-generation anthistamines is that they tend to produce substantially less drowsiness than the original antihistamine drugs (such as Benadryl), and they last longer, so you only have to take them once a day.

How Antihistamines Work

Your body has 4 different types of receptors on your cells. Receptors are like communication pathways that allow signalling from outside the cell to the inside of the cell. These four histamine receptors allow the body to communicate important information to the cells of your body to maintain healthy functioning. Histamines cause the following things to occur:

  • swelling
  • activation of pain receptors
  • itchiness
  • redness
  • contraction of smooth muscles (present in airways, intestines, bladder, and blood vessels)

Antihistamines are medications that block the communication pathway between the body and the cell by occupying the space that the histamines would have used to signal the cell. Antihistamines there for prevent swelling, pain activation, itchness, redness, and smooth muscle contraction from occurring. As such, antihistamines can be useful in treating:

You should know that while antihistamines can treat the above conditions, they may not be the preferred or safest option. For example antihistamines are not the best option for treating anaphylaxis and bronchoconstriction.

Who Can Take Zyrtec?

Zyrtec can be taken by most healthy individuals who are at least 6 months old and have never had an allergic reaction to Zyrtec or any medication including the generic form, cetirizine HCl.

Zyrtec is a pregnancy category B. This means that studies on pregnant animals showed no adverse effects on the fetus but studies on humans have not been conducted. Talk to your doctor before taking Zyrtec if you are pregnant. It is generally recommended that you not take Zyrtec while breastfeeding. Tell your doctor about any medications you are taking including prescription, over-the-counter medication and herbs before starting Zyrtec.

How To Take Zyrtec?

Zyrtec comes in several different doses and forms including tablets, chewable tablets and syrup. It is taken once per day, usually in 5 or 10mg doses, but this varies depending on your age and weight. For this reason it is very important to read the instructions very carefully before taking Zyrtec. If you are confused speak with a pharmacist.

Side Effects of Zyrtec

Side effects include: drowsiness, dry mouth, dizziness and pharyngitis (inflammation of the throat which may cause tonsillitis or sore throat--it is interesting to note that this effect may actually be caused by your allergies and not the medication).

Symptoms of an allergic reaction to Zyrtec include: swelling, hives, difficulty breathing, or wheezing and require immediate medical attention. Less common side effects included a stomach ache, irritability in small children, headache, diarrhea, and bloody noses. Read the package insert for a more complete list of side effects.

Other Precautions

Zyrtec (and other antihistamines) do not prevent the serious allergic reactions known as anaphylaxis, and should not be used as a substitute for the epinephrine which doctors often prescribe for this condition.


Day JH, Briscoe MP, Rafeiro E, et al. Randomized double-blind comparison of cetirizine and fexofenadine after pollen challenge in the Environmental Exposure Unit: duration of effect in subjects with seasonal allergic rhinitis. Allergy Asthma Proc 2004; 25:59.

Day JH, Briscoe M, Widlitz MD. Cetirizine, loratadine, or placebo in subjects with seasonal allergic rhinitis: effects after controlled ragweed pollen challenge in an environmental exposure unit. J Allergy Clin Immunol 1998; 101:638.

O'Mahoney, L, Akdis, M & Akdis, CA. (2011). Regulation of the immune response and inflammation by histamine and histamine receptors. Journal of Allergy and Clinical Immunology. 128(6):1153–1162

Simons, FER & Akdis, CA. (2014). Middleton's Allergy: Principles and Practice. Histamine and H 1 Antihistamines. Accessed: July 30, 2016 from https://www.clinicalkey.com (Subscription Required).

Edited by Richard N. Fogoros, MD

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