Pregnancy is a special physiological condition in which pharmacotherapy is of particular concern because the physiology of pregnancy affects the pharmacokinetics of the drugs used, and some drugs can reach the fetus and cause harm. Drug therapy cannot be completely avoided during pregnancy and may be dangerous because some women go into pregnancy with medical conditions that require ongoing and occasional treatment (such as asthma, epilepsy, and high blood pressure). Also, new medical problems can appear during pregnancy and old problems (such as migraines and headaches) that require drug treatment can worsen.