On Oct. 26, 1951, the Durham-Humphrey Amendment, also known as the Prescription Drug Amendment, was signed into law by President Harry S. Truman. The act defined two specific categories for medications: legend (prescription) and over-the-counter (OTC).

The amendment was co-sponsored by former vice president and Minnesota senator Hubert H. Humphrey Jr. (D), a pharmacist in South Dakota before entering politics, and Carl Durham (D), a pharmacist who represented North Carolina.