Which phase of a clinical trial involves testing the efficacy of a drug or device?

The phase of a clinical trial that specifically focuses on testing the efficacy of a drug or device is Phase II. This phase is critical as it typically involves a larger group of participants who have the condition that the drug or device is intended to treat. The primary objective during Phase II is to determine whether the treatment shows a beneficial effect on the condition, while also continuing to evaluate its safety and side effects.

In Phase I, the primary focus is on assessing the safety and tolerability of the treatment in a small group of participants, without a strong emphasis on efficacy. Phase III expands the participant group even further to confirm effectiveness, monitor side effects, and compare the treatment against standard or equivalent treatments, but it is dependent on the findings of Phase II to proceed. Phase IV occurs after the drug or device has been approved, focusing on post-marketing surveillance to monitor long-term effects and overall effectiveness in the general population.