For many years, the US Food and Drug Administration (FDA) has used five categories (A, B, C, D, and X) to describe a drug's potential for causing adverse effects during pregnancy ( table 2 ) [ 5 ]. The categories are based upon the results of animal studies, human data, and consideration of whether the benefit of the drug's use during pregnancy outweighs the risk. The FDA has begun the phase-out of pregnancy risk categories from prescription drug labeling and now requires information from available human and animal studies about (1) known or potential maternal or fetal risks, (2) dose adjustments needed during pregnancy and the postpartum period, and (3) benefit/risk considerations [ 6 ]. While new medications include this information, the process of updating existing medications will likely take several years. In the interim, it is useful to have an understanding of the various categories.