In 1951, Sanger and McCormick approached Gregory Pincus (a researcher of biology and hormone use) about conducting research on the use of a contraceptive hormone. They provided the funds necessary for the research. Following the grant, Pincus (pictured to the right) traveled to Mexico in search of a chemist (Russell Marker) and a lab in which to work. This began the search for progesterone. Progesterone is frequently known as “the pregnancy hormone,” and plays a key role in the female reproductive system. Scientifically, progesterone “is formed in the ovary upon the release of a mature egg. If the egg becomes fertilized, progesterone and estrogen act together to maintain the pregnancy. These hormones also regulate the menstrual cycle in the non pregnant female.”  The first chemist known to create an imitation of this hormone was Russell Marker. In Mexico, many developments took place that allowed Pincus to begin studying the effects of progesterone in lab animals.
The production of Progesterone
The first lab to begin developing progesterone was through the efforts of Marker and Dr. Somlo, who set up the company called “Syntex,” in Mexico. When Marker became dissatisfied with the pay he was receiving from his research, he left the company to begin his own competing company called “Botanica-Mex.” In 1946, this company merged with a European company to become “Hormosynth.” Meanwhile, another chemist, Carl Djerassi, joined the team at Syntex. In its early forms, progesterone would only be effective in large doses and when injected into the body. With the support of Syntex, Djerassi hoped to develop something that would be more effective and more easily used than progesterone. He later created norethindrone. It served the same purpose of progesterone, but was much stronger when taken orally and in smaller doses. Near the same time however, a Chicago pharmaceutical company known as G.D. Searle, manufactured a similar product: norethynodrel. The patents for the two products were filed in 1951 and 1953, respectively. 
Research and Trials
Gregory Pincus first began experimenting with progesterone on Rabbits. In order to be able to include women in clinical trials, he would need the supervision of a medical doctor. In 1952, Pincus met Dr. Rock (pictured to the right), an expert on the female reproductive system. When Pincus first met Rock, Rock was conducting his own research with the synthetic hormone. His goal however, was just the opposite. Dr. Rock had been testing progesterone in women with the hopes that it would help them to become pregnant. When they combined their research, they began using the oral form of progesterone developed by Colton and G.D. Searle (it was suggested to have fewer side effects than its counterpart created by Syntex). The drug that they began testing became known as Enovid.
The first clinical trials that were carried out on women were done so in Boston over a period of a few months. The women who participated were given the pill for twenty days and then told to stop taking the pill for about a week. During this week, their periods would resume, and the first trials were noted as a success. In order for the drug to be released, however, more long term studies would need to take place and a larger pool of women would need to be studied. The long term studies were moved to Puerto Rico, where they would be less prohibited by law to study and publish the results of these contraceptive trials. Once in Puerto Rico the study became known as “The study of the physiology of progesterone in women.” Throughout these studies, Sanger and McCormick were heavily invested in the process. They corresponded with one another and with the doctors with concern over the success of the trials. In a letter to Margaret Sanger, McCormick commends the decision to move testing to Puerto Rico where there would be fewer governmental and religious interference in the process saying that “…for an enlargement of the testing to work of Drs. Pincus and Rock the Welfare Department in Puerto Rico is considered to be the most practical place.”
In 1957 two companies that produced the oral version of the progesterone hormone approached the FDA for approval to release the drug to the public. It was approved with the limitations that it was only to be used to correct female menstrual problems and could only be taken with the prescription of a doctor. Three years later the headlines read “U.S. Approves Pill for Birth Control,” and on May 9, 1960 the FDA approved the use of Enovid as safe for contraceptive uses. The FDA approved the pill based on judgments of safety, they did not consider morality or any religious conflicts that may have resulted. This task would be left up the American Public, as they would now begin to grapple with the idea of an easy and more effective means to control the birth rate.