BACKGROUND:Public attention and recent US Congressional activity has intensified focus on escalating medication prices. However, the actual cost of medication use extends beyond the up-front cost of purchasing medicines. It also encompasses the additional medical costs of morbidity and mortality resulting from nonoptimized medication regimens, including medication nonadherence. OBJECTIVES:Applying the most current nationally representative data sources, our goal was to estimate the cost of prescription drug-related morbidity and mortality in the United States. METHODS:Total costs of nonoptimized prescription drug use and average pathway costs for a patient who experienced a treatment failure (TF), a new medical problem (NMP), or a TF and NMP were modeled in Microsoft Excel (Microsoft Corporation, Redmond, WA) and TreeAge Pro Healthcare, v2014 (TreeAge Software, Inc, Williamstown, MA), respectively. RESULTS:The estimated annual cost of prescription drug-related morbidity and mortality resulting from nonoptimized medication therapy was $528.4 billion in 2016 US dollars, with a plausible range of $495.3 billion to $672.7 billion. The average cost of an individual experiencing TF, NMP, or TF and NMP after initial prescription use were $2481 (range: $2233, $2742), $2610 (range: $2374, $2848) and $2572 (range: $2408, $2751), respectively. CONCLUSIONS:The estimated annual cost of drug-related morbidity and mortality resulting from nonoptimized medication therapy was $528.4 billion, equivalent to 16% of total US health care expenditures in 2016. We propose expansion of comprehensive medication management programs by clinical pharmacists in collaborative practices with physicians and other prescribers as an effective and scalable approach to mitigate these avoidable costs and improve patient outcomes.