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Table 3 NIH clinical trial phases for human subject research

From: Twenty years and still counting: including women as participants and studying sex and gender in biomedical research

“Biomedical clinical trials of an experimental drug, treatment, device, or behavioral intervention may proceed through four phases” [18]
Phase 1 Tests a new intervention in a small group of human subjects for the first time to evaluate efficacy and safety.
Phase 2 Tests the efficacy of a new intervention in a larger group (usually several hundred) to further evaluate efficacy and safety.
Phase 3 Compares a new intervention to standard or to other experimental interventions in large groups (several hundred to thousands) to determine efficacy and to monitor and collect data on adverse effects.
Phase 4 Assesses after-market effectiveness in the general population and collects data on any adverse effects associated with widespread use.