Zyrtec (cetirizine) is taken as a single dose once a day, with or without food. The standard adult dose is 10 mg. You can take it at any time of day, though many people prefer the evening since it can cause drowsiness.
Adult and Teen Dosing
If you’re 12 or older, the recommended dose is 5 mg or 10 mg once daily, depending on how severe your symptoms are. Most people take 10 mg. You can start at 5 mg to see how you respond, especially if you’re concerned about drowsiness, then move up to 10 mg if needed. Do not exceed 10 mg in a 24-hour period.
Children’s Dosing by Age
Children ages 6 and up can take 5 mg to 10 mg once daily. For younger children ages 2 to 5, the dose is 2.5 mg to 5 mg once daily. Children’s Zyrtec syrup makes it easy to measure smaller doses since each milliliter contains 1 mg. So a 2.5 mg dose is 2.5 mL of syrup, and a 5 mg dose is 5 mL.
Children under 2 should not take Zyrtec unless specifically directed by a pediatrician.
Available Forms
Zyrtec comes in several formats, and the one you pick mostly comes down to personal preference:
- Standard tablets and liquid gels: Swallowed whole, taken once every 24 hours.
- Chewable tablets: Available in 2.5 mg and 10 mg strengths. The lower-dose version can be taken every 12 to 24 hours; the 10 mg version is once every 24 hours.
- Dissolve tabs: Melt on the tongue with or without water, once every 24 hours. Convenient when you don’t have a drink handy.
- Children’s syrup: A liquid given every 12 to 24 hours depending on the dose.
- Zyrtec-D: A combination product that includes a decongestant. This one is taken every 12 hours, not every 24, so don’t confuse it with regular Zyrtec.
All forms can be taken with or without food.
Best Time of Day to Take It
There’s no single “correct” time. The FDA labeling notes that you can vary the time of administration to suit your needs. That said, cetirizine causes drowsiness in roughly 14% of people (compared to about 6% on a placebo), so if it makes you sleepy, taking it before bed turns that side effect into an advantage. If it doesn’t affect your alertness, morning is perfectly fine and may give you coverage during peak pollen hours.
The key is consistency. Taking it at roughly the same time each day keeps a steady level in your system.
Drowsiness and Alcohol
Cetirizine is classified as a “non-drowsy” antihistamine, but it’s the most sedating of the second-generation options. You may feel sleepy, dizzy, or less sharp, particularly at 10 mg. Alcohol amplifies these effects, increasing dizziness, drowsiness, and difficulty concentrating. Avoid or limit alcohol while taking it, especially until you know how it affects you.
Kidney Problems and Dose Adjustments
Your kidneys are responsible for clearing cetirizine from your body. If you have reduced kidney function, the standard 10 mg dose can build up and increase the risk of side effects. Adults and teens with significant kidney impairment are typically advised to reduce their dose to 5 mg daily. The same principle applies to children with kidney issues. If you know you have kidney disease, check with your pharmacist or doctor before starting.
Pregnancy and Breastfeeding
International guidelines consider cetirizine an acceptable choice during breastfeeding. Small occasional doses pass very little into breast milk. One study measured the maximum a fully breastfed infant would receive at about 1.9% of the mother’s weight-adjusted dose, which is well below the threshold of concern. However, larger or more frequent doses may cause drowsiness in the infant or reduce milk supply. In a study of 31 women taking cetirizine daily, about a third noticed a perceived drop in milk production over several days.
If you’re pregnant, cetirizine is generally considered one of the preferred antihistamines, but confirm the choice with your prenatal care provider since recommendations can vary by trimester.
What to Do if You Miss a Dose
If you forget a dose, take it as soon as you remember. If it’s almost time for your next dose, skip the missed one and return to your regular schedule. Don’t double up to make up for it. Since Zyrtec provides about 24 hours of coverage per dose, a missed dose simply means a gap in symptom relief rather than any safety concern.