Medication adherence is vital for the effective management and prognosis of chronic diseases. This study aimed to assess medication adherence levels among patients with various chronic conditions and to identify factors influencing adherence behavior. A systematic review and meta-analysis were conducted, searching major databases for studies published between 2010 and 2024. Eligible studies assessed medication adherence using validated measures such as self-reporting, pill counts, pharmacy refill records, and electronic monitoring devices. The review included studies from different geographic regions and diverse patient populations. Results showed a wide range of adherence rates among patients with chronic diseases, with an overall adherence rate of 80%. Factors influencing medication adherence included socioeconomic status, education level, health literacy, complexity of medication regimens, side effects, and patient-provider communication. Interventions such as patient education, reminder systems, and simplification of medication regimens demonstrated potential in improving adherence. However, further research is needed in diverse patient populations. Enhancing medication adherence among patients with chronic diseases remains a critical aspect of healthcare delivery to optimize health outcomes and reduce healthcare costs.