After a drug's initial safety has been established, Phase II trials are commenced. In this stage, the drug is administered to a larger group of people (100-300), allowing to determine its efficacy, or whether its effect on the body is significant enough to warrant further testing.
In Phase III trials, the experimental study drug or treatment is given to large groups of patients (1,000-10,000) to confirm its efficacy and define the risk/benefit profile, in comparison to the most commonly used treatments, in order to allow its approval by the international regulatory .