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Table 2 FDA clinical study phases for new drug applications

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

“The new drug application is the vehicle through which drug sponsors formally propose that the FDA approve a new pharmaceutical for sale in the United States” [17]
Phase 1 Emphasizes the assessment of safety - how a new drug is metabolized and excreted, how a drug should be given, how often, at what dose. It is usually conducted with a small number of healthy volunteers.
Phase 2 Continues to test safety and begins to evaluate how well a drug works by comparing it with a different treatment, usually a placebo or another drug. Conducted in a larger sample.
Phase 3 Tests the efficacy of a new drug in comparison to the current standard, evaluates dosages and overall risk-benefit of the drug. Conducted in a large numbers of volunteers.
Phase 4 Studies post-approval use of a drug if the FDA judges the need to gather population data on drug safety.