Cetirizine (Zyrtec) is classified as a Pregnancy Category B medication by the FDA, meaning animal studies have shown no harm to a fetus and it is generally considered one of the safer antihistamine options during pregnancy. That said, it is not the first-choice antihistamine recommended by major medical organizations, and the timing of use matters.
What Category B Means for You
The FDA assigns Category B to drugs that have been tested in pregnant animals at high doses without causing birth defects, but lack large, well-controlled human studies. For cetirizine specifically, animal testing at doses 40 to 220 times the standard human dose showed no signs of harm to the developing fetus in mice, rats, or rabbits. Because no drug can be tested the same way in pregnant humans, the official label recommends using it “only if clearly needed,” which is standard language for Category B medications.
A small prospective study conducted by the Motherisk program followed 39 women who took cetirizine during pregnancy (37 of them in the first trimester) and found no differences in pregnancy outcomes compared to unexposed women. Broader research on antihistamines as a class has also not identified increased fetal risk when these medications are used at any point during pregnancy.
Where Cetirizine Falls in Treatment Guidelines
The American College of Obstetricians and Gynecologists (ACOG) and the American College of Allergy, Asthma and Immunology (ACAAI) recommend older, first-generation antihistamines as the initial choice for pregnant women. Chlorpheniramine and tripelennamine top their list because they have the longest track record of use in pregnancy.
Cetirizine and loratadine are recommended as second-line options, specifically after the first trimester, for women who don’t respond to or can’t tolerate those older antihistamines. The reason cetirizine isn’t first-line has less to do with known dangers and more to do with the fact that the older medications simply have more decades of human pregnancy data behind them. If you’re already past your first trimester and your allergies are significantly affecting your quality of life, cetirizine is considered an appropriate option.
First Trimester Considerations
The first trimester is when major organ systems form, so any medication use during this window gets extra scrutiny. A large study examining antihistamine use in early pregnancy did not find meaningful support for previously suggested links between antihistamines and major birth defects. However, because the data is less robust for cetirizine than for older antihistamines during this specific window, guidelines suggest starting with chlorpheniramine if you need allergy relief in the first 12 weeks. The main downside of chlorpheniramine is that it causes more drowsiness than cetirizine, which is why many women prefer the newer option.
Common Side Effects During Pregnancy
Cetirizine is a second-generation antihistamine, meaning it causes less sedation than older options like diphenhydramine (Benadryl) or chlorpheniramine. Still, some drowsiness is possible, and pregnancy fatigue can amplify that effect. Dry mouth is another common side effect, which can be more noticeable if you’re already dealing with pregnancy-related dehydration. Sticking to the standard 10 mg daily dose minimizes these effects.
Cetirizine While Breastfeeding
Cetirizine does pass into breast milk, but in very small amounts. Studies show that a breastfed infant would receive roughly 1.8% of the mother’s weight-adjusted dose, with a worst-case estimate of about 3.4%. These numbers are well below the 10% threshold that pharmacologists typically use to flag concern. International guidelines consider cetirizine an acceptable choice for breastfeeding mothers.
One caution: larger or more frequent doses may cause drowsiness in the infant or reduce milk supply, especially early on before breastfeeding is well established. Combination products that pair cetirizine with a decongestant like pseudoephedrine (sold as Zyrtec-D) carry a higher risk of affecting milk supply and are best avoided while nursing.
How Cetirizine Compares to Other Options
- Chlorpheniramine: The top recommended antihistamine in pregnancy due to its long safety record. Works well but causes more drowsiness. Available over the counter.
- Loratadine (Claritin): Shares the same second-line status as cetirizine in pregnancy guidelines. Also Category B, also recommended after the first trimester. Choosing between the two often comes down to which one controls your symptoms better.
- Diphenhydramine (Benadryl): Also Category B with a long track record in pregnancy. Causes significant drowsiness, which limits daytime use but can be helpful at bedtime if allergies are disrupting sleep.
All of these are considered safer than decongestants containing pseudoephedrine, which have raised more concern during pregnancy, particularly in the first trimester. If your main symptom is nasal congestion rather than sneezing or itchy eyes, saline sprays or nasal steroid sprays may be a better starting point.
Practical Takeaways
Cetirizine has no proven harmful effects in pregnancy based on available evidence. It sits in a reassuring safety category and has been used by many pregnant women without documented problems. The reason guidelines place it as a second-line option is about data volume, not red flags. If you were already taking cetirizine when you found out you were pregnant, the existing evidence does not suggest a reason for alarm. Going forward, the decision about which antihistamine to use depends on your trimester, how well you tolerate the older alternatives, and how much your allergy symptoms are affecting your daily life.