In Phase I clinical trials, how many healthy volunteers are typically used to determine the safety of a drug?

• A. Between 20 and 80 volunteers
• B. Between 5 and 15 volunteers
• C. Between 100 and 200 volunteers
• D. Between 200 and 1000 volunteers

Answer: (D)

Phase I trials aim to establish safety, tolerability, and basic pharmacokinetics in humans using a small, carefully selected group of healthy volunteers. This small group is enough to detect common adverse effects and to get initial PK data without exposing many people to potential risks. The typical size is on the order of a few dozen to around a hundred volunteers—roughly 20 to 80, sometimes up to about 100. Larger numbers, in the hundreds or thousands, are not characteristic of Phase I; they belong to later-stage trials where safety, efficacy, and broader population effects are evaluated. So, the usual range is about 20–80 healthy volunteers (often up to 100) for Phase I safety assessment.