At what visit should all unused investigational agents be returned to the sponsor?

All unused investigational agents should be returned to the sponsor at the termination site visit. This visit serves as the formal conclusion of a clinical trial at a specific site, and it is during this time that final reconciliations of investigational products are conducted. Returning any remaining investigational agents ensures that they are accounted for, which is critical for compliance with regulatory requirements and the principles of Good Clinical Practice.

In contrast, the other visit types serve different purposes. For instance, a startup site visit primarily focuses on initiating the study protocol, ensuring that the site is ready to begin enrollment and data collection. Monitoring site visits are conducted periodically throughout the study to ensure protocol compliance and data integrity but do not involve the concluding activities associated with the termination visit. Interim site visits occur at various times during the trial to review data and study progress but likewise do not pertain to the final return of investigational materials. Thus, the termination site visit is the designated time for the comprehensive assessment and return of unused investigational agents.