Nonadherence to medications can limit the effectiveness of treatments for a variety of conditions. Adherence is particularly important for chronic conditions, such as cardiac disease, that require long-term use of medications. Decades' worth of studies1,2 have reported that many patients are not adherent to cardiac medications, such as antihypertensives and statins, with adherence often below 50%. Earlier studies measured adherence by identifying patients filling a first prescription and then following claims records for subsequent refills. Patients who never filled their first prescription were not captured. Accordingly, prior studies of adherence systematically overestimated the proportion of patients actually taking medications as prescribed.