Where are unused investigational agents expected to be returned to the sponsor?

The correct answer highlights the importance of returning unused investigational agents to the sponsor during the termination site visit. This visit typically occurs at the completion of a clinical trial or when a study is being closed. During this process, all remaining investigational products must be accounted for and returned to ensure proper documentation and compliance with regulatory requirements.

Returning unused agents at this time allows the sponsor to manage the investigational product effectively, including proper disposal, documentation, and consideration for future research or studies. This ensures participant safety, as any leftover product is not inadvertently used outside of the controlled study setting.

Returning investigational products at other times, such as during a prestudy or site initiation visit, does not align with the flow of the clinical trial and does not ensure that all products are returned in a final, organized manner. Periodic site visits may include checks or interim returns, but the formal and complete return typically occurs at the termination site visit, solidifying its role as the critical juncture for this aspect of trial management.