Expanded controlled and uncontrolled studies. They are performed after preliminary evidence of drug effectiveness has been obtained. They are intended to gather additional information about effectiveness and safety that is needed to evaluate the overall benefit-risk relationship of the drug and to provide adequate basis for physician labeling. These studies usually include anywhere from several hundred to several thousand subjects.
Phase III studies are large double-blind randomized controlled trials on large patient groups (1000-3000 or more) and are aimed at being the definitive assessment of the efficacy of the new therapy, especially in comparison with currently available alternatives.
In Phase III, the new treatment is compared with commonly used treatments and monitored for long-term side effects.