Evaluating drug efficacy and side effects.

• A. Phase 3 clinical trials
• B. Phase 2 clinical trials
• C. Phase 1 clinical trials
• D. NDA

Answer: (B)

In this stage of drug development, the focus is on whether the drug actually works in patients and what adverse effects it may cause, while also refining the appropriate dose. These mid-stage trials enroll more participants than early safety studies and often use a control group to provide a preliminary estimate of efficacy relative to placebo or standard therapy. They help establish dose–response relationships and characterize the safety profile in a patient population, setting up the larger, definitive studies to come. By contrast, early-phase trials concentrate on safety, pharmacokinetics, and tolerability in a small group; late-phase trials (the large, confirmatory studies) test efficacy and safety in a broader population to confirm results and detect rarer adverse effects; and the NDA is the regulatory submission that compiles all data to seek approval.