What Dr. Pincus and colleagues developed was a pill containing estrogen and progestin, synthetic hormones similar to those produced naturally in a woman's body. The pill works primarily by suppressing the release of eggs from a woman's ovaries. Although the pill was widely welcomed, it wasn't long before concerns were raised about possible serious side effects. As early as 1961, suspicions arose in the United States and England that the pill might predispose some women to heart attack and stroke. Evidence of blood clotting had been reported in a few women taking the pill.
Blood clots can cause life-threatening heart attacks and strokes.
In 1965, spurred by further reports, FDA awarded a research contract to a scientist at the Johns Hopkins School of Hygiene and Public Health to investigate exactly how widespread the problem was. The committee was also directed to review existing data for clues to the pill's potential to cause cancer of the breast, cervix and endometrium. It called for a large, case-control study of the relationship between oral contraceptives and blood clotting. As for cancer, the advisory committee concluded the pill hadn't been in use long enough to draw valid conclusions about its carcinogenic effects. For example, it would be at least another 10 years before the risk of uterine cancer could be accurately assessed.