Which of the following ALWAYS requires packaging in a child-proof container?

Controlled substances require packaging in a child-proof container due to their potential for misuse and the need to protect children from accidental ingestion. The packaging is a critical safety measure mandated by law to minimize the risk of harm. Child-proof containers are designed to be difficult for children to open while still being accessible to responsible adults, thus providing an effective barrier against accidents.

In contrast, not all prescription-only drugs necessarily require child-proof packaging. For example, some prescription medications in smaller dosages or specific types may be exempt from these requirements under certain conditions, which is why the other choices do not consistently require such packaging. Therefore, the requirement for child-proof containers specifically applies to controlled substances as a standard safety precaution.