What is the primary purpose of a Phase II trial in drug development?

The primary purpose of a Phase II trial in drug development is to determine a drug's short-term risks and safety. During this stage, researchers focus on evaluating the drug's efficacy and safety profile in a larger group of participants after initial safety has been confirmed in Phase I trials.

Phase II trials are specifically designed not only to assess how well the drug works (its efficacy) but also to gather more comprehensive information about its safety, including any adverse effects that may not have been evident in the smaller Phase I trials. This allows for a better understanding of the risk-benefit profile of the drug as it moves towards larger-scale testing in Phase III trials.

The other options may pertain to aspects of drug development, but they are not the primary focus of Phase II trials. For example, testing drug efficacy in large populations pertains more to Phase III trials, establishing long-term effects would typically be evaluated in post-marketing studies or later phases, and assessing pharmacokinetics is often a focus of both Phase I and early Phase II but does not encapsulate the main goal of the Phase II trial.