Table 2.

Clinical Trial Phases

Phase I. Researchers test an experimental drug or treatment in a small group of people (20–80) for the first time to evaluate its safety, determine a safe dosage range, and identify side effects. Many phase 1 trials are testing an agent for the first time in humans

Phase II. Researchers test the experimental study drug or treatment in a larger group of people (100–300) to see if it is effective and to further evaluate its safety.

Phase III Researcher test the experimental study drug or treatment in a larger group still (1,000 or more) to confirm its effectiveness, monitor side effects, compare it to commonly used treatments, and collect information that will allow the experimental drug or treatment to be used safely. Phase 3 trials are usually randomized controlled clinical trials.

Phase IV Researchers collect additional information after an agent is approved and marketed regarding its risks, benefits, and use in various populations over a longer period of time.