A medical product development is a long and expensive process that can take more than ten years until approval. It is divided in consecutive phases:
Phase I : The goal of Phase 1 studies is to evaluate how the drug interacts with the human body, the side effects associated with increased dosages, and could also gather early information about how effective it is and determine the drug administration which have limited risk and a maximum of possible benefits. These trials are conducted on healthy volunteers (tens). After Phase 1 and in case of good safety profile, the product can go through Phase II.
Phase II : The goal of Phase 2 studies is to determine the optimal dosing of the medicinal product and to test the efficacy and complete the safety data. These trials are conducted on few hundred patients. If the evidence of effectiveness is shown, the Phase III can start.
Phase III : The goal of Phase 3 studies is to confirm previous results with the new medicinal product in order to show the efficacy and evaluate the efficacy/tolerance to a specific population. These trials are done on several hundred up to thousands patients.
Complete dossier and results are then submitted to the competent health authorities (as for example the European Agency of Medicines (EMA) in Europe or the FDA (US Food & Drug Administration) in the US) and in case of marketing license authorization, the new medicinal product is brought to market.
Phase IV : Once on the market, Phase 4 studies are carried out for post-marketing safety monitoring with close watch on the side effects : it is pharmacovigilance.