Medication adherence is crucial for effective patient care and achieving clinical goals. Poor adherence leads to poor health outcomes, increased healthcare costs, and unnecessary expenditures. This review article discusses various methods for measuring medication adherence, including subjective and objective measures. Subjective measures, such as self-report and clinician assessments, provide explanations for nonadherence, while objective measures, like pill count, electronic monitoring, and biochemical tests, offer more precise records of medication-taking behavior. However, no single measure is perfect, and a combination of methods is often recommended for accurate results. The article categorizes adherence measures into direct and indirect methods. Direct measures, such as drug concentration testing and electronic medication packaging (EMP) devices, are highly accurate but can be intrusive and costly. EMP devices, like the Medication Events Monitoring System (MEMS), are objective and useful for validating other measures, but they are expensive and may not be suitable for all patient populations. Pill count is an indirect, objective measure that compares the number of doses taken with the total received, but it can underestimate adherence and is less reliable for chronic conditions. Subjective measures, such as patient interviews and self-report questionnaires, are less reliable but more cost-effective and easier to administer. They include tools like the Brief Medication Questionnaire (BMQ), Hill-Bone Compliance Scale, and the Eight-Item Morisky Medication Adherence Scale (MMAS-8), which are widely used in research and clinical practice. These measures can identify barriers to adherence and predict nonadherence but may be influenced by patient bias or psychological factors. The article emphasizes the importance of using a multimeasure approach to accurately assess medication adherence, as no single method is sufficient. Combining objective and subjective measures can provide more reliable results and help identify the reasons behind nonadherence. However, the complexity and cost of multimeasure approaches can be a challenge in clinical settings. The review also highlights the need for further research to develop more effective and accurate adherence measures, particularly for specific populations and conditions. Overall, the choice of adherence measure should consider reliability, cost, practicality, and the specific needs of the patient population.Medication adherence is crucial for effective patient care and achieving clinical goals. Poor adherence leads to poor health outcomes, increased healthcare costs, and unnecessary expenditures. This review article discusses various methods for measuring medication adherence, including subjective and objective measures. Subjective measures, such as self-report and clinician assessments, provide explanations for nonadherence, while objective measures, like pill count, electronic monitoring, and biochemical tests, offer more precise records of medication-taking behavior. However, no single measure is perfect, and a combination of methods is often recommended for accurate results. The article categorizes adherence measures into direct and indirect methods. Direct measures, such as drug concentration testing and electronic medication packaging (EMP) devices, are highly accurate but can be intrusive and costly. EMP devices, like the Medication Events Monitoring System (MEMS), are objective and useful for validating other measures, but they are expensive and may not be suitable for all patient populations. Pill count is an indirect, objective measure that compares the number of doses taken with the total received, but it can underestimate adherence and is less reliable for chronic conditions. Subjective measures, such as patient interviews and self-report questionnaires, are less reliable but more cost-effective and easier to administer. They include tools like the Brief Medication Questionnaire (BMQ), Hill-Bone Compliance Scale, and the Eight-Item Morisky Medication Adherence Scale (MMAS-8), which are widely used in research and clinical practice. These measures can identify barriers to adherence and predict nonadherence but may be influenced by patient bias or psychological factors. The article emphasizes the importance of using a multimeasure approach to accurately assess medication adherence, as no single method is sufficient. Combining objective and subjective measures can provide more reliable results and help identify the reasons behind nonadherence. However, the complexity and cost of multimeasure approaches can be a challenge in clinical settings. The review also highlights the need for further research to develop more effective and accurate adherence measures, particularly for specific populations and conditions. Overall, the choice of adherence measure should consider reliability, cost, practicality, and the specific needs of the patient population.