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In page Gregory G. Pincus:

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In order to prove the safety of "the pill," human trials had to be conducted. These were initiated among infertility patients of John Rock in Brookline, Massachusetts, using progesterone in 1953 and then three different progestins in 1954. Puerto Rico was selected as a trial site in 1955, in part because there was an existing network of 67 birth control clinics serving low-income women on the island. Trials began there in 1956 and were supervised by Edris Rice-Wray and Celso-Ramón García.[citation needed]