Which law required that drugs actually be efficacious?

The Kefauver Harris Amendment, passed in 1962, is pivotal in establishing the requirement that drugs must not only be safe but also effective for the claimed uses. Prior to this amendment, the Food and Drug Administration (FDA) focused primarily on the safety of drugs without a stringent mandate for efficacy. This amendment arose from concerns regarding the thalidomide tragedy, where a drug was marketed without sufficient evidence of its effectiveness, leading to severe consequences.

The Kefauver Harris Amendment sharpened the regulatory framework by necessitating that pharmaceutical companies provide substantial evidence of a drug's effectiveness through clinical trials before receiving approval. This transformed the landscape of drug approval, ensuring that only those medications proven to provide a therapeutic benefit could be marketed, thus protecting public health and improving patient outcomes.

The other laws mentioned do have significant roles in drug regulation, such as the Federal Food, Drug, and Cosmetic Act, which established the FDA's authority, or the Controlled Substances Act, which focuses on the regulation of narcotics, but they do not specifically mandate that drugs must be proven effective in the way the Kefauver Harris Amendment does.