Before an investigational drug is approved for use by the Food & Drug Administration (FDA) and becomes available by prescription, it must be evaluated through several phases of clinical trials. Before human studies can begin, pre-clinical trials are conducted in animals to determine a drug's safety profile.
Phase I clinical trials are the first studies conducted in people that measure the safety of a drug, including how it is absorbed, metabolized and secreted within a person's body. A small number of healthy clinical research volunteers (20 - 100) are enrolled.
Phase II clinical trials measure the safety and effectiveness of a drug and enroll up to several hundred patient volunteers. These are people diagnosed with the condition the drug is being tested for, i.e., type 2 diabetes, depression, etc. Many phase II trials use a process called randomization, in which some patients receive the investigational drug and others receive the standard treatment or placebo (a drug that looks like the investigational drug but contains no active ingredients) as part of a control group.
Often these studies are "blinded" so that neither the patient nor the research team knows which patients received the investigational drug. A blinded randomization process allows researchers to gather unbiased comparative information about the effectiveness of the investigational drug.
Phase III clinical trials are randomized and blinded trials enrolling several hundred to several thousand patient volunteers. These trials provide more information about how the investigational drug works, including information on side effects and long-term use. At the conclusion of this phase, a pharmaceutical company can request FDA approval to market the drug.
Phase IV clinical trials are conducted after a drug has been FDA-approved for use and can be obtained by a prescription. These trials compare the newly approved drug with similar drugs currently in use, to monitor the new drug's long-term effectiveness and impact on a patient's quality of life. Phase IV trials can also determine a drug's cost-effectiveness compared to other newly approved drugs.