Who is responsible for explaining the correct use of the investigational product(s) to participants?

• A. The sponsor's marketing team.
• B. The ethics committee.
• C. The participant's family.
• D. The investigator or a designated person.

Answer: (D)

The key idea is that the person who explains how to use the investigational product to participants must be the investigator or someone they have trained and designated. In Good Clinical Practice, the investigator holds overall responsibility for the trial at the site and must ensure participants receive clear, accurate instructions on how to take the investigational product, how to store it, what to do if a dose is missed, and what to do in case of adverse effects. This instruction can be delegated to a qualified, trained team member, but the investigator remains accountable for the information given and for confirming that the participant understands it. The sponsor’s marketing team and the ethics committee do not provide day-to-day instructions on product use, and a participant’s family is not part of the trial conduct.