Taking Zyrtec for Allergies

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

The chief advantage of second-generation antihistamines is that they tend to produce substantially less drowsiness than older antihistamine drugs (such as Benadryl). They also last longer, so you only need to take them once a day.

Girl with allergies in field of flowers blowing her nose
Echo / Cultura / Getty Images

How Antihistamines Work

Your body has four different types of histamine receptors on your cells. Receptors are like communication pathways that allow signaling 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 therefore prevent swelling, pain activation, itchiness, 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.

Talk to your healthcare provider before taking Zyrtec if you are pregnant. Animal studies have shown no risk to fetuses, but controlled human studies are lacking.

It is generally recommended that you not take Zyrtec while breastfeeding.

Tell your healthcare provider about any medications you are taking before starting Zyrtec, including prescription and over-the-counter medicines, nutritional supplements, and herbal products.

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 10 mg 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

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 healthcare providers often prescribe for this condition.

6 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Randall KL, Hawkins CA. Antihistamines and allergyAust Prescr. 2018;41(2):41–45. doi:10.18773/austprescr.2018.013

  2. Panula P, Chazot PL, Cowart M, et al. International Union of Basic and Clinical Pharmacology. XCVIII. Histamine ReceptorsPharmacol Rev. 2015;67(3):601–655. doi:10.1124/pr.114.010249

  3. Maintz L, Novak N. Histamine and histamine intolerance. Am J Clin Nutr. 2007;85(5):1185-96. doi:10.1093/ajcn/85.5.1185

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Additional Reading
  • Simons, FER & Akdis, CA. (2014). Middleton's Allergy: Principles and Practice. Histamine and H 1 Antihistamines.

  • 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.
  • 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.
  • 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

By Kristin Hayes, RN
Kristin Hayes, RN, is a registered nurse specializing in ear, nose, and throat disorders for both adults and children.