Just as there are different types of clinical trials, there are also different steps, or phases. This step-by-step process helps scientists evaluate if a new drug, medical device or treatment is safe and effective to use on humans. Each phase of a clinical trial has a different purpose and is designed to answer a specific question. The phases of clinical trials are as follows:
1. Phase I Trials
Phase I trials tell researchers if a new drug, device or treatment is safe. This is the first step in testing a new approach on people. Phase I trials are initially conducted on a small group of people (20 to 80). In these studies, scientists determine the safest dose range of a new drug and how it should be given (by mouth or in the vein or muscle).
2. Phase II Trials
Once researchers discover that a new approach is safe to use on humans, they must then answer the question "does it work?" Phase II trials are conducted on a larger group of people (100 to 300) to further evaluate the safety of the treatment and to determine how well it works.
3. Phase III Trials
Phase III trials involve large groups of people (1,000 to 3,000) and are done to determine if the new treatment is more effective, or has less side effects, than the standard (currently approved) method. This phase answers the question "does it work?"
4. Phase IV Trials
Phase IV trials are generally done in the post-marketing stages of the treatment, after the U.S. Food and Drug Administration (FDA) has approved it for general use. Phase IV studies are conducted on hundreds to thousands of people, but are less common than phase I, II or III trials.