What are the phases of drug development and clinical trials?

Drug development progresses through defined stages: 1) Discovery - target identification, lead compound discovery, in vitro testing. 2) Preclinical - animal studies for safety, toxicology, pharmacokinetics (ADME). IND application to FDA. 3) Phase I trials - first-in-human, 20-100 healthy volunteers, safety and dosing (6-12 months). 4) Phase II trials - 100-500 patients with disease, efficacy and side effects (1-2 years). 5) Phase III trials - 1000-5000 patients, large-scale efficacy, comparison to existing treatments (2-4 years). NDA/BLA submission. 6) FDA review and approval (6-12 months). 7) Phase IV - post-market surveillance for long-term effects. Total development typically takes 10-15 years with ~$1-2 billion cost and <10% success rate from preclinical to approval.