Senator Estes Kefauver had already been investigating pharmaceutical prices, promotion, and the quality of evidence for therapeutic claims. Thalidomide gave new urgency to that debate. The resulting Kefauver–Harris Drug Amendments became law in October 1962; they were a congressional reform shaped by many participants, not legislation written by Kelsey alone.
Manufacturers now had to provide substantial evidence of effectiveness as well as safety before marketing. Adequate and well-controlled studies became central to that evidence, and affirmative FDA approval replaced the earlier arrangement under which an application could take effect without an explicit approval decision.
The reforms also strengthened authority over investigational drugs and informed consent, adverse-reaction reporting, manufacturing standards, and prescription-drug advertising. The FDA's account of a century of drug regulation explains these changes. Safety review and proof of therapeutic benefit were related responsibilities, but they answered different questions.