What actions should the investigator take to ensure correct use of the investigational product(s) by each subject?

• A. The investigator or a person designated should explain correct use to each subject and check adherence at intervals appropriate for the trial.
• B. Provide written instructions only; no verbal explanation.
• C. Check adherence only at the end of the trial.
• D. Adherence is not required.

Answer: (A)

Ensuring correct use of the investigational product hinges on clear education and ongoing adherence monitoring. The investigator or a designated, trained staff member should explain to each subject exactly how to use the IP—how to dose, when to take, route of administration, storage, handling, and what to do if a dose is missed—then confirm that the subject understands. After that, adherence should be checked at intervals that fit the trial’s dosing schedule and risk level, so issues are caught early and safety and data integrity are preserved. Relying only on written instructions can lead to misunderstandings, and checking adherence only at the end misses important safety signals and data quality concerns. Adherence is a fundamental requirement in GCP, not something optional.