Drug Repurposing: Accelerating New Therapeutic Discoveries from Old Molecules (1990 – 2025)

Drug repurposing, also known as drug repositioning or reprofiling, involves discovering new therapeutic indications for approved, withdrawn, or shelved drugs whose pharmacological and toxicological properties are already well characterized [1]. Traditional drug discovery requires 10–15 years and billions of dollars for a single molecule, with a success rate below 10 percent [2]. Repurposing leverages known safety and pharmacokinetic profiles to reduce risk, cost, and time, offering a strategic shortcut to bring therapies rapidly to patients [3]. The concept has evolved from serendipitous observations—such as the antihypertensive drug minoxidil being developed into a hair-growth agent—to a systematic data-driven approach integrating bioinformatics, network pharmacology, and artificial intelligence [4]. Between 1990 and 2025, advances in genomics, transcriptomics, and big-data analytics transformed repurposing into a predictive discipline [5]. During the COVID-19 pandemic, repurposing gained global visibility as existing antivirals and immunomodulators were tested under emergency use [6]. This review traces the historical development of repurposing, global and Indian milestones, computational strategies, and future perspectives for regulatory harmonisation [7].