ADVERSE DRUG REACTIONS: A COMPREHENSIVE REVIEW

Abstract

Adverse drug reactions (ADRs) represent a major challenge in clinical practice and public health worldwide. They contribute significantly to patient morbidity, mortality, prolonged hospitalization, and increased healthcare costs. An ADR is defined by the World Health Organization (WHO) as a response to a medicinal product that is noxious and unintended and occurs at doses normally used in humans for prophylaxis, diagnosis, therapy, or modification of physiological function. ADRs may be predictable and dose-dependent (Type A) or unpredictable and unrelated to dose (Type B), with further modern classifications expanding to Types C, D, E, and F. Risk factors include patient-related variables (age, genetics, comorbidities), drug-related factors (polypharmacy, narrow therapeutic index), and system-related issues (medication errors, lack of monitoring). Pharmacovigilance systems play a pivotal role in detection, assessment, understanding, and prevention of ADRs. This review discusses definitions, classification, epidemiology, mechanisms, risk factors, diagnosis, prevention strategies, and reporting systems, emphasizing their clinical and regulatory importance.