Phase II trials are best described as controlled clinical studies conducted in no more than several hundred subjects to evaluate effectiveness for a specific indication and to determine short-term adverse effects and risks.

• A. Phase II trials are controlled clinical studies conducted in no more than several hundred subjects.
• B. Phase II trials evaluate long-term safety in thousands of patients.
• C. Phase II trials determine market authorization.
• D. Phase II trials compare two drugs in Phase III settings.

Answer: (A)

Phase II trials are designed to see if a drug shows effectiveness for a specific disease and to characterize short-term safety, after initial safety has been established in Phase I. They use a controlled design to compare outcomes in patients who receive the drug versus a control condition, but they involve more participants than Phase I yet remain smaller than Phase III—typically a few hundred people. This size allows researchers to explore dose responses, get a clearer signal of efficacy, and identify short-term adverse effects and risks, without committing to the large-scale, long-term safety data that comes later.

These studies aren’t the step that grants market authorization—that occurs after Phase III and regulatory review. They also aren’t primarily about long-term safety, which is evaluated in Phase III and in post-marketing surveillance. So the description matches the typical purpose, size, and focus of Phase II trials: assessing preliminary effectiveness for a specific indication while monitoring short-term safety in a moderate-sized patient group.