Phase III study is conducted and tested in several hundred to several thousand patients. This large scale testing provides the pharmaceutical company and the FDA with a more thorough understanding of the drug’s effectiveness, benefits, and the range of possible adverse reactions. Most phase III studies are randomized and blinded trials. Phase III studies typically last several years. 70 to 90 percent of drugs that enter phase III studies successfully complete this phase of testing. Once a phase III study is successfully completed, a pharmaceutical company can request FDA approval for marketing the drug.