Which law first required the statement "Caution: Federal law prohibits dispensing without a prescription" on drug product packaging?

The statement "Caution: Federal law prohibits dispensing without a prescription" was first required on drug product packaging by the Durham-Humphrey Amendment of 1951. This amendment to the Federal Food, Drug, and Cosmetic Act established a distinction between prescription and over-the-counter medications. It recognized that certain drugs required a healthcare professional's oversight for safe use and, consequently, needed to be dispensed only with a prescription. By mandating that the caution statement be prominently displayed, the law aimed to inform consumers of the legal requirements pertaining to prescription medications and to emphasize the importance of appropriate medical supervision in the dispensing of these drugs. This was a significant step in regulating pharmaceuticals and ensuring patient safety.

Other laws mentioned, such as the Food, Drug, and Cosmetic Act of 1938, established the foundation for drug regulation but did not specifically address this caution statement. The Controlled Substances Act of 1970 focused on regulating controlled substances and their distribution, while the Drug Enforcement Administration Act of 1973 dealt with enforcement mechanisms for controlled substances rather than labeling requirements. This makes the Durham-Humphrey Amendment the correct answer regarding the specific requirement for the caution statement on drug packaging.