Which clinical trial phase uses healthy volunteers to test safety and dosage?

• A. Phase I
• B. Phase II
• C. Phase III
• D. Phase IV

Answer: (A)

In early human testing, the priority is safety and how the drug behaves in the body. This phase uses healthy volunteers to evaluate tolerability, identify side effects, and determine safe dosage ranges—including how the drug is absorbed, distributed, metabolized, and excreted (pharmacokinetics) and how it affects the body (pharmacodynamics). By testing in people without the disease, researchers can get a clearer picture of safety without confounding factors from the condition being treated.

This approach distinguishes it from later stages. In subsequent phases, the drug is given to patients with the target condition to assess efficacy and further safety in a real-world disease context (phase II) and then in larger populations to confirm effectiveness and monitor rare or long-term side effects (phase III). After approval, ongoing safety monitoring in the general population occurs (phase IV).