FDA Classification: Class A In controlled studies, no indication of fetal harm was seen in women in the third trimester (and no evidence of harm in the subsequent 6 months), and there may be minimal fetal effects. Grade B In animal reproduction studies (no controlled studies in pregnant women), no fetal effects were seen. Adverse effects were demonstrated in animal reproduction studies and were not confirmed in women in the third trimester (and there was no evidence of harm in the subsequent 6 months). J. Zhang, Department of Dermatology, Peking University Shenzhen Hospital Adverse effects on the fetus (teratogenic or embryonic killing) have been demonstrated in class C animal studies, but no controlled studies have been conducted in pregnant women. This class should only be applied after weighing the benefits to the pregnant woman outweigh the harms to the fetus. Class D is used when there is clear evidence of harm to the fetus and, despite the harm, there is an absolute benefit to the pregnant woman with the drug (for example, when the pregnant woman is threatened with death or has a serious illness and the application of other drugs, although safe, is ineffective). Class X has been shown in animal or human studies to cause fetal abnormalities, and the application of this class of drugs in pregnant women is clearly not beneficial. This class of drugs is contraindicated in patients who are pregnant or about to become pregnant. Note: Antihistamines should be contraindicated in early pregnancy and Class B antihistamines such as loratadine, cetirizine, and first-generation antihistamines (e.g., paracetamol, cyproheptadine, benadryl, etc.) may be used as appropriate in mid- to late-pregnancy, and no antihistamines are recommended for lactation.