In which development phase are normal, healthy volunteers typically administered a new drug?

In the context of drug development, Phase I studies are specifically designed to assess the safety, tolerability, pharmacokinetics, and pharmacodynamics of a new drug. During this phase, the drug is administered to a small group of normal, healthy volunteers. The primary objective is to determine how the drug behaves in the body, including how it is absorbed, distributed, metabolized, and excreted.

Additionally, Phase I trials are crucial for identifying any potential side effects and understanding the drug's safety profile, which informs subsequent clinical trial phases. The focus on healthy volunteers helps to minimize variability that could be caused by underlying medical conditions, thereby allowing researchers to establish a clearer understanding of the drug's effects in a controlled population.

In contrast, other phases, such as Phase II, typically involve patients with the targeted condition to evaluate efficacy and further understand safety, while Phase III expands the participant pool to confirm efficacy and monitor adverse reactions in a larger population. Phase IV occurs post-marketing, primarily focused on long-term effects and additional side effects in the general population. Thus, Phase I is the correct answer for the administration of a new drug to healthy volunteers.