Is Zyrtec (cetirizine) safe while breastfeeding?

What does the evidence say about Zyrtec while breastfeeding?

1. Cetirizine gets into breast milk in small amounts, and most reports show no problems for nursing babies exposed to it this way; the medication is also thought to have a lower chance of causing drowsiness for both the breastfeeding parent and the baby compared with older antihistamines. 1
2. In pharmacokinetic studies, breastfed infants received an estimated 1.8% to 3.4% of the mother's weight-adjusted cetirizine dose, and international breastfeeding guidelines list cetirizine as an acceptable antihistamine choice when one is needed. 2
3. In a study of 31 women taking cetirizine, 10 reported a perceived decrease in milk supply over the prior three days, though the connection has not been proven, and larger doses or more prolonged use may add to any effect, particularly when combined with a decongestant such as pseudoephedrine. 2
4. A single 60 mg dose of pseudoephedrine, the decongestant in Zyrtec-D, caused a 24% average decrease in milk production over the following 24 hours in a small study, a much more clearly established effect on supply than cetirizine has on its own. 3
5. Studies involving more than 1,300 pregnancies exposed to cetirizine did not show an increased chance of birth defects, and available data during breastfeeding have not found a higher chance of miscarriage or other pregnancy complications either. 4

How Zyrtec changes by nursing stage

• Early weeks. In the early weeks of breastfeeding, before supply is fully established, it's worth being extra cautious with any medication that could affect milk production. Choosing plain cetirizine over a Zyrtec-D combination product avoids the pseudoephedrine-related supply risk during this window.
• Established nursing. Once breastfeeding is well established, occasional or regular plain cetirizine is generally considered compatible, and international guidelines list it as an acceptable antihistamine option if you need one for allergies.
• Weaning. In later, well-established breastfeeding, occasional use of Zyrtec-D is less likely to meaningfully affect supply than it would be in the earlier weeks, though many providers still suggest trying plain cetirizine or a nasal option first.