An FDA reviewer blocked Thalidomide from the US market

Why the application stayed on her desk

In 1960, drugmaker Richardson-Merrell sought FDA approval to sell thalidomide in the United States under the name Kevadon. The drug was already being sold in several other countries as a sedative and was promoted for nausea during pregnancy. FDA reviewer Frances Kelsey was responsible for assessing the company’s application—not simply checking whether the drug seemed useful, but deciding whether its evidence adequately showed it was safe.

Kelsey repeatedly asked for stronger evidence, particularly about how thalidomide might affect a developing fetus. Reports of nerve damage in some adults also raised concerns. The company pressed for approval, but the unanswered questions mattered: a medicine taken by a pregnant person could reach the embryo, and harm during a narrow period of development might not be apparent in routine testing.

A drug’s danger depended on timing

Thalidomide can disrupt the growth of a fetus’s limbs and other organs when exposure occurs early in pregnancy. The resulting birth defects could be severe, including arms or legs that were very short or did not develop normally. Because pregnancy may not yet be recognized, a medicine marketed for nausea could expose an embryo before a patient knew to avoid it.

The company’s application never received U.S. approval. That prevented ordinary commercial sales, though it did not mean no one in the country was exposed: investigational samples had been distributed to doctors, and some patients took them. Kelsey’s review helped limit exposure, rather than eliminate it.

The review changed what approval demanded

The thalidomide disaster abroad made the danger unmistakable and intensified scrutiny of how medicines were tested and approved. In 1962, Congress strengthened U.S. drug law, requiring manufacturers to provide evidence of effectiveness as well as safety and establishing stronger expectations for clinical testing and informed consent.

Kelsey’s decision mattered because it kept an inadequately supported application from becoming an approved product while the risks were still unclear. The lasting consequence was broader: drug approval came to depend more firmly on evidence, not a company’s assurances or a medicine’s popularity elsewhere.