The objectives of this report are to summarize the content and status of transporter-related postmarketing requirement (PMR)/postmarketing commitment (PMC) studies in new drug applications (NDAs) approved by the U.S. Food and Drug Administration (FDA) and to discuss the reasons for requesting such studies and the impact of PMR/PMC study results on labeling to guide the optimal use of the drugs. Multiple data sources were searched to collect information on transporter-related PMR/PMC studies between January 1999 and May 2015. A total of 40 transporter-related PMR/PMC study requests were issued for 35 NDAs. Among these PMR/PMC studies, 27 requested studies related to P-glycoprotein. As of May 31, 2015, 34 transporter-related PMR/PMC studies (85%) are considered “fulfilled” (per the FDA's PMR/PMC website), and 22 (65%) resulted in labeling updates. The majority of the PMR/PMC studies are for drugs in the therapeutic areas of anti-infectives, oncology, and neurology. The results from PMR/PMC studies are important for dosing optimization and are often included in the updated labeling. Because a significant lag time is anticipated between drug approval and PMR/PMC fulfillment, NDA applicants are encouraged to include transporter-related assessments in clinical drug development programs for drug products.