In July 1962, the Food and Drug Administration sent an urgent message to its field offices with an assignment it said was “one of the most important we have had in a long time.”

Overseas, thousands of babies in Germany, England and other countries were being born with severe defects tied to their mothers’ use of thalidomide, a drug widely taken for insomnia, morning sickness and other ailments.

Meanwhile, the federal government sought to figure out what had happened in the United States, and how many babies had been affected.

The drug was not approved in the United States in the 1960s, but as many as 20,000 Americans were given thalidomide in the 1950s and 1960s as part of two clinical trials operated by the American drug makers Richardson-Merrell and Smith, Kline & French.