Zyrtec’s active ingredient is cetirizine hydrochloride, an antihistamine that comes in a standard adult dose of 10 mg per tablet. Beyond that single active compound, the tablet contains several inactive ingredients that hold the pill together, coat it, and help it dissolve. If you’re checking for potential allergens or just want to know exactly what you’re swallowing, here’s the full breakdown.
The Active Ingredient: Cetirizine
Cetirizine hydrochloride is a second-generation antihistamine, meaning it was designed to relieve allergy symptoms without causing as much drowsiness as older antihistamines like diphenhydramine (the active ingredient in Benadryl). It works by blocking H1 receptors, which are proteins found on nerve endings, smooth muscle cells, and glandular cells throughout your body. When you encounter an allergen like pollen or pet dander, your immune system releases histamine. Histamine latches onto those H1 receptors and triggers the familiar cascade of sneezing, itching, runny nose, and watery eyes. Cetirizine competes with histamine for those same receptors, essentially blocking it from doing its job.
Cetirizine also appears to reduce the migration of certain immune cells (eosinophils) to areas of allergic reaction in the skin, which helps explain why it’s effective for hives and not just nasal symptoms. A single 10 mg dose provides 24 hours of relief, which is why Zyrtec is taken once daily.
Inactive Ingredients in the Adult Tablet
The standard Zyrtec 10 mg film-coated tablet contains these inactive ingredients:
- Lactose monohydrate: a milk sugar used as a filler to give the tablet bulk
- Microcrystalline cellulose: a plant-derived fiber that acts as a binder
- Colloidal silicon dioxide: prevents ingredients from clumping together
- Croscarmellose sodium: helps the tablet break apart in your stomach so the drug can absorb
- Magnesium stearate: a lubricant that keeps the tablet from sticking to manufacturing equipment
- Hypromellose and polyethylene glycol: form the thin film coating on the outside of the tablet
- Titanium dioxide: a white pigment that gives the coating its color
None of these ingredients are therapeutic. They exist purely to make the tablet stable, easy to swallow, and capable of releasing cetirizine at the right rate in your digestive system.
Allergen Concerns: Lactose, Gluten, and Dyes
The adult tablet does contain lactose monohydrate. If you have severe lactose intolerance or a milk allergy, this is worth noting, though the amount is small. People with mild lactose intolerance rarely have issues with the trace quantities found in a single tablet, but it’s not zero.
Zyrtec chewable tablets are marketed as dye-free, and the children’s syrup is labeled dye-free, sugar-free, and alcohol-free. The standard adult film-coated tablet uses titanium dioxide for its white color rather than any FD&C dyes. Zyrtec’s labeling does not make a specific gluten-free claim, so if you have celiac disease, you may want to contact the manufacturer directly for confirmation.
Children’s Zyrtec Syrup
The liquid formulation designed for children contains cetirizine hydrochloride at a concentration of 5 mg per 5 mL (one teaspoon). Its inactive ingredients are quite different from the tablet:
- Anhydrous citric acid
- Flavors
- Propylene glycol
- Purified water
- Sodium benzoate (a preservative)
- Sorbitol solution (a sugar alcohol used as a sweetener)
- Sucralose (an artificial sweetener)
The syrup contains no sugar, no alcohol, and no dyes. Sorbitol is the primary sweetener, which is generally well tolerated but can cause digestive discomfort in some children if consumed in large amounts. At the doses used in a single teaspoon of allergy syrup, this is unlikely to be an issue.
Chewable Tablets
Zyrtec chewable tablets share the same active ingredient but use a different set of inactive ingredients to create a chewable texture and flavor. These include betadex, corn starch, lactose monohydrate, magnesium stearate, mannitol, silicified microcrystalline cellulose, and sucralose. Like the syrup, chewable tablets are labeled dye-free. They do still contain lactose.
What’s in Zyrtec-D
Zyrtec-D is a separate product that adds a nasal decongestant. Each extended-release tablet contains 5 mg of cetirizine hydrochloride (half the dose of a regular Zyrtec tablet) plus 120 mg of pseudoephedrine hydrochloride. Pseudoephedrine narrows blood vessels in the nasal passages to relieve stuffiness, something cetirizine alone doesn’t do well. Because it contains pseudoephedrine, Zyrtec-D is kept behind the pharmacy counter in most states and requires showing identification to purchase, even though it doesn’t need a prescription.
The reduced cetirizine dose in Zyrtec-D is paired with the extended-release format, so the drug releases gradually rather than all at once. This means Zyrtec-D and regular Zyrtec are not interchangeable, and taking both simultaneously would result in more cetirizine than intended.