In the NDA Process, which phase involves the largest number of volunteers for testing efficacy?

The phase that involves the largest number of volunteers for testing efficacy is Phase III. This phase is crucial in the drug development process as it focuses on confirming the drug's effectiveness and safety across a diverse population.

During Phase III trials, hundreds to thousands of participants are enrolled, allowing researchers to gather substantial data on the drug's effectiveness compared to standard treatments or placebos. This large sample size helps ensure that the results are robust and can be generalized to a broader population. It is designed to detect any adverse effects and confirm the therapeutic benefits of the medication prior to it being submitted for regulatory approval.

In contrast, the earlier phases involve fewer participants and focus more on aspects like safety and dosage rather than efficacy in a larger, more varied group. Preclinical studies, which occur before any human testing, involve laboratory and animal studies to assess the drug's viability and safety but do not include human volunteers at all.