[Evaluation of the efficacy of a drug: from discovery to market].

To move from a chemical entity to a real drug, preclinical trials have to be followed by phase I human studies to evaluate human toxicity, phase II studies to demonstrate the pharmacological activity in healthy volunteers and patients, followed by phase III studies to evaluate the real therapeutic efficacy. Then new drug authorization is granted for a product that shows good pharmaceutical quality and a positive risk-benefit ratio. However, full knowledge of a new drug is available only after several years of clinical use.