Prescription and over-the-counter medications use is common in pregnancy, with the average pregnant patient in the US and Canada using more than two drugs during the course of their pregnancy (Mitchell et al., 2001). One reason for this is that some women enter into pregnancy with pre-existing medical conditions, such as diabetes, hypertension, asthma, and others, that require pharmacotherapy; and for many others, gestational disorders (hyperemesis gravidarum, gestational diabetes, preterm labor) complicate women’s pregnancies and require treatment. Moreover, virtually the majority of organ systems are affected by substantial anatomic and physiologic changes during pregnancy, with many of these changes beginning in early gestation. Many of these alterations significantly affect the pharmacokinetic (absorption, distribution, metabolism, and elimination) and pharmacodynamic properties of different therapeutic agents (Pacheco et al., 2013). Therefore, it becomes essential for clinicians and pharmacologists to understand these pregnancy adaptations, in order to optimize pharmacotherapy in pregnancy, and limit maternal morbidity because of over- or under-treating pregnant women. The purpose of this review is to summarize some of the physiologic changes during pregnancy that may affect medication pharmacokinetics.