Chlorcyclizine hydrochloride is a histamine H1 antagonist. IC50 & Target: Histamine H1^[1] In Vivo: Pregnant rats administered 30, 60, and 90mg/kg Chlorcyclizine during the sensitive period for palate development survived until scheduled sacrifice on Gestation Days (GDs) 17 or 21. The rats administered 60 or 90mg/kg Chlorcyclizine have transient adverse clinical signs (chromorhinorrhea, red peri-oral substance, urogenital staining, and scant stool) and a concomitant body weight loss of 7% and 11%, respectively, over the dosing interval. Rats administered 30mg/kg Chlorcyclizine do not exhibit any adverse clinical signs, but do not gain weight over the dose interval as would be expected during pregnancy. Based on the testing facility’s historical control database (16 studies, n=380). pregnant rats typically gain about 6% body weight from GDs 12 to 15^[1].