Medication adherence is crucial for optimal treatment outcomes, yet many patients struggle to follow their prescribed regimens, impacting patients, families, and healthcare systems. Measurement of adherence is vital for effective care planning and intervention. This review explores medication adherence challenges and measurement methods, including therapeutic drug monitoring (TDM), medication event monitoring system (MEMS), analysis of adherence in insurance/pharmacy database, pill counts, and self-reports, each with its advantages and limitations. This review advocates a partnership-based approach to adherence, stressing standardized reporting and team-based care. Adherence is influenced by many factors such as complex regimens, packaging, patient perspectives, side effects. Effectively addressing these factors is crucial for improving patient outcomes. In summary, medication adherence is vital but complex. The article covers various adherence measurement methods to promote medication adherence as an important matter (Tab. 5, Fig. 2, Ref. 91).