What is required on a prescription label for a controlled substance?

The requirement for including the caution that "Federal Law prohibits the transfer of this drug to any person other than the patient for whom it was prescribed" on a prescription label for a controlled substance is crucial for both legal and safety reasons. This statement serves to remind patients that controlled substances are subject to strict regulations due to their potential for abuse and dependency. By including this warning, the label communicates the importance of using the medication only as prescribed and reinforces the legal constraints surrounding the dispensing and use of such medications.

Including this caution helps ensure that patients understand the serious implications of sharing prescription medications, which could lead to misuse and potential legal consequences. This aligns with the intent of the Controlled Substances Act, which aims to regulate the distribution and use of substances that have a high potential for abuse.

The other elements that might be found on a prescription label—such as a prescription number or warnings about drowsiness—are important for patient safety and record-keeping but do not specifically address the legal aspects tied to controlled substances in the same way. Likewise, while the instruction to keep the medication away from children is an important safety measure, it is not uniquely required for controlled substances, thus making option C the most pertinent answer in the context of the question.