Type 2 diabetes mellitus (T2DM) is a chronic metabolic disorder characterized by insulin resistance, progressive β-cell dysfunction, and persistent hyperglycaemia, imposing a substantial clinical, social, and economic burden worldwide. Effective diabetes management requires long-term pharmacotherapy, lifestyle modification, regular monitoring, and sustained patient engagement. Medication adherence is therefore a critical determinant of therapeutic effectiveness and glycaemic control. This review examines medication adherence in T2DM from clinical, behavioural, pharmaceutical, and healthcare-system perspectives. It discusses the concepts of adherence, compliance, persistence, and non-adherence, along with their prevalence, determinants, barriers, measurement methods, and clinical consequences. Evidence indicates that suboptimal adherence to antidiabetic therapy remains common, although reported rates vary considerably according to study population, treatment regimen, adherence definition, and measurement method. Poor adherence has been associated with inadequate glycaemic control, increased risk of diabetes-related complications, reduced quality of life, and greater healthcare utilization and economic burden. Major determinants include treatment complexity, polypharmacy, adverse effects, socioeconomic constraints, medication cost and availability, psychological factors, limited health literacy, and inadequate healthcare access. Particular emphasis is placed on pharmacist-led interventions, patient education, behavioural strategies, medication counselling, treatment simplification, follow-up, and digital health technologies. Evidence from India further highlights the influence of socioeconomic and healthcare-access barriers on medication-taking behaviour. Overall, medication adherence should be considered a dynamic and multifactorial behaviour rather than solely a patient related factor. An individualized, patient-centred, and multidisciplinary approach involving pharmacists and other healthcare professionals is essential to improve adherence and optimize diabetes outcomes. Future research should emphasize standardized adherence definitions, validated measurement approaches, culturally appropriate interventions, and longer-term evaluation, particularly within Indian healthcare settings.

KEYWORDS: Type 2 Diabetes Mellitus, Medication Adherence, Medication Non-adherence, Antidiabetic Drugs, Glycaemic Control, Pharmacist, Diabetes Self-management, Digital Health.