Clinical trials involving new drugs are commonly classified into four phases. Each phase of the drug approval process is treated as a separate clinical trial. The drug-development process will normally proceed through all four phases over many years. If the drug successfully passes through Phases I, II, and III, it will usually be approved by the national regulatory authority for use in the general population. Phase IV is 'post-approval' studies.
Phase I includes 20 to 100 healthy volunteers or individuals with the disease/condition. This study typically lasts several months and its purpose is safety and dosage. Phase II includes a larger number of individual participants ranging 100-300, and phase III includes Approximately 1000-3000 participants to collect more data about the drug.[6] 70% of drugs advance to the next phase.[7]
Before pharmaceutical companies start clinical trials on a drug, they conduct extensive pre-clinical studies