Drug repurposing is the strategy of finding new medical uses for existing drugs that are already approved or in development. Because the safety, pharmacokinetics, and manufacturing of these compounds are at least partly known, repurposing can reduce cost, shorten development timelines, and lower failure rates compared with discovering entirely new molecules.

Many repurposing efforts start with systematic screening of large libraries of approved or shelved drugs against disease models. High throughput screening, phenotypic assays, and computational approaches such as molecular docking and network analysis are used to identify candidates that act on relevant targets or pathways. Integrating clinical data, including real world evidence from electronic health records and adverse event databases, can reveal unexpected beneficial effects of drugs used for other indications.

Cancer, infectious diseases, and neurological disorders are prominent areas of application. In oncology, researchers are investigating common non cancer drugs like anti inflammatories, anti diabetics, and antihypertensives for their effects on tumor growth, angiogenesis, and metastasis. In infectious disease, repurposed antivirals, antiparasitics, and antibiotics are tested for activity against emerging pathogens. For neurodegenerative diseases, compounds originally developed for cardiovascular or metabolic conditions are examined for their ability to modulate inflammation, oxidative stress, or protein aggregation.

Despite its advantages, repurposing faces obstacles. Intellectual property issues, lack of commercial incentives for off patent drugs, and the need for rigorous clinical trials in new indications can slow progress. Regulatory pathways exist to support new uses, but tailored funding models, public private partnerships, and better data sharing are crucial to fully exploit the potential of drug repurposing as a fast, cost efficient route to new therapies.