In the late 1950s and early 1960s, thalidomide was marketed in several countries as a sedative and treatment for morning sickness in pregnancy. Reports began to accumulate in Europe and elsewhere of a sharp increase in infants born with phocomelia—markedly shortened or absent limbs—and other congenital malformations. Although the drug had been widely prescribed overseas, the United States had not granted full approval for thalidomide’s general use. On February 12, 1962, amid growing international concern and emerging clinical reports linking the drug to birth defects, U.S. regulatory authorities moved to prevent the drug’s approval and distribution. The action followed a period of review in which independent investigators, clinicians, and some within the pharmaceutical industry raised questions about the drug’s safety in pregnancy. While thalidomide had been submitted for consideration in the United States, the U.S. Food and Drug Administration’s careful scrutiny and the intervention of reviewers helped keep widespread use from taking hold domestically. The U.S. response contrasted with earlier and broader use in other countries, where inadequate regulatory controls and less rigorous pre-release testing contributed to greater exposure among pregnant women. Internationally, the thalidomide tragedy ultimately affected thousands of children and prompted nationwide investigations, litigation, and changes in public health policy. In the United States, the ripple effects of the 1962 decision were substantial. The episode strengthened calls for more robust drug safety regulations and helped galvanize legislative reforms. Later in 1962, Congress passed amendments to the Food, Drug, and Cosmetic Act that expanded the FDA’s authority to require proof of drug efficacy and safety before approval, and to demand more stringent clinical testing and labeling—measures intended to reduce the risk of similar tragedies. Medical researchers and public health officials also intensified surveillance of congenital malformations and adverse drug effects. The thalidomide case became a touchstone in medical ethics and pharmacovigilance, underscoring the need for rigorous clinical trials, careful assessment of drugs intended for use in pregnancy, and transparent reporting of adverse outcomes. Decades later, thalidomide has been reintroduced in controlled settings for a limited set of indications—such as certain complications of leprosy and some cancers—under strict risk-management programs designed to prevent exposure during pregnancy. Those later uses reflect both advancement in understanding of the drug’s mechanisms and the long-lasting impact of the early safety failures that led to its initial ban. Historical assessments of the period emphasize that regulatory caution in the United States likely limited domestic harm but did not prevent the international catastrophe. Scholarship and contemporary reviews document both the scientific uncertainties of the time and the human costs that drove regulatory reform. Where details are disputed—such as the precise sequence of corporate submissions and internal deliberations—histories note disagreement among company records, regulatory testimony, and later analyses. Nevertheless, the connection between thalidomide exposure in pregnancy and severe congenital defects is well established and remains a seminal example in the history of drug safety.