Phase III Trials: If a new treatment does show some promise in a Phase II trial, often the next step is to compare it to an old treatment to see which is better, or to add it to an old treatment, and see whether the new combination is better. In some cases, there is no usual treatment, and so the new treatment is compared to no treatment. Phase III trials usually involve higher numbers of patients, perhaps hundreds or even thousands, and often take place at the same time at many institutions, sometimes in many countries. In addition to testing the effectiveness of a new treatment approach, often Phase III trials help to provide more information about side effects and tolerability of treatments, and their impact on quality of life. 

Safety features in Phase III trials