Summary
- Phase 1 mainly looks at safety and how the body handles something, usually in small groups.
- Phase 2 looks at whether it seems to work and at the right amount, in larger groups.
- Phases 3 and 4 test in large groups and then keep watching after approval.
Section 1.0
Phase 1: first look
Small groups, often a few dozen people, to learn how something is tolerated and how the body processes it. Some Phase 1 studies include healthy volunteers; others involve people with a condition.
Section 2.0
Phase 2: early signs
A larger group, often a few hundred, to look for early signs it works and to refine the amount and schedule while continuing to watch safety.
Section 3.0
Phase 3: the big comparison
Hundreds to thousands of people, often compared with a standard approach or a placebo. Results from this phase are a large part of what regulators review.
Section 4.0
Phase 4: after approval
Once something is available, studies may continue to watch for rarer effects and long-term outcomes in broader groups. Group sizes and details differ by study.
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