Treatment trials are generally conducted in phases. This is what happens during each phase:
Phase I is the first time humans receive the new drug or other treatment under investigation.
In Phase II, the safety and effectiveness are studied in volunteers who have the condition for which the treatment is being considered.
Several hundred to several thousand people may be enrolled in Phase III clinical trials. These trials are conducted over a period of years in hospitals, medical centers, and private physicians' offices across the United States. They also are conducted by large medical centers and government-supported organizations, such as the NIH (National Institute of Health) and the Veterans Administration.
In Phase III, the investigational treatment is compared to a standard therapy currently used to treat the condition and the overall benefits and risks of the treatment under investigation are evaluated. The data gathered from Phase III trials provides a better understanding of the treatment's effectiveness, benefits, and potential side effects.
Volunteers are divided into two groups: a Control Group and a Study Group. The volunteers in the control group do not receive the investigational treatment. They receive either a currently accepted treatment or a placebo. The volunteers in the study group receive the treatment under investigation.
Once Phase III testing is complete, a pharmaceutical company can submit a drug to the FDA. The FDA uses the data to help determine whether or not to approve the drug.
Phase IV trials are not always conducted. When they are, they usually take place after the treatment receives FDA approval and is available to the public. During a Phase IV trial, long-term safety and effectiveness, side effects that may not have been apparent during Phase III, and optimal usage are evaluated. Hundreds to thousands of volunteers may participate in a Phase IV trial.