In 1912, a nurse named Margaret Sanger was dreaming about pills — The Pill, to be exact.

“She had this thing in her mind, like a fantasy,” says Jonathan Eig, author of "The Birth of the Pill: How Four Crusaders Reinvented Sex and Launched a Revolution." What if there was some miracle tablet that would let women turn on and off their reproductive systems?

The problem wasn't necessarily the science — it was the scientists. Finding people willing to work on a “women’s issue” was no easy task, especially one especially one as controversial — and illegal, in many states — as birth control.

"This was just such a neglected area of science," Eig says. “Men were interested in the atom bomb, and they weren’t interested in The Pill. Men were calling the shots."

But men weren’t the only ones with cash, as Sanger soon found out. Her idea resonated with Katharine Dexter McCormick, a wealthy suffragette, who agreed to finance the project. “[McCormick] really believed, after working in the suffrage movement, that the next step for women’s equality was being able to control the number of children they had,” Eig explains.

The next step was finding a scientist — a hormone expert, to be exact. “By the late 1940s and early 1950s, we’re beginning to understand hormones,” Eig says. Scientists were realizing it was possible to regulate the body’s functions by supplying it with additional hormones.

In 1951, Sanger and McCormick met their man. His name was Gregory Pincus, a physiologist with a serious chip on his shoulder. He'd been fired by Harvard and was running a small lab out of Worcester, Massachusetts.

"When Sanger met him, he says, ‘Of course I can make a birth control pill. Why would that be difficult?'" Eig says.

Pincus’s concept for the drug was simple: When a woman is pregnant, her body releases a hormone called progesterone that stops her from ovulating. Pincus developed a pill made of progesterone, and tested it successfully on animals in the lab.

Then came the hard part: finding human subjects. This is where the group had to get devious, Eig says. Even talking about birth control in Massachusetts was illegal at the time.

Together with John Rock, a gynecologist, the group identified women being treated by doctors for infertility. They gave them high doses of The Pill, calling it “a rest for their reproductive systems,” and tracked their ovulation.

“It convinced Pincus this was safe,” Eig says. “They weren’t dropping dead, and they weren’t growing third arms."

That's not to say it was all smooth. "They were suffering some serious side effects, like nausea and dizziness," Eig says. "But [Pincus] didn’t really care about that because they weren’t getting pregnant.” He also tested the drug in insane asylums — on both women and men. “It wasn’t pretty,” Eig admits.

At this point, Pincus was convinced the drug worked, but they still needed thousands more test subjects before they could submit it for approval. That’s when they decided to go to Puerto Rico.

In the slums of San Juan, Puerto Rico's capital city, Pincus and Rock found willing candidates and a government more amenable to new methods of “population control,” as they saw it.

They began dispensing very high doses of The Pill, dismissing patients' complaints of severe side effects. While the methods were controversial, the Puerto Rican trials made one thing clear to the two doctors – The Pill worked.

By the time they were ready to submit the drug to the FDA in 1957, momentum for the Pill was already off the charts. When the FDA approved it for menstrual regulation later that year, “women were lining up for it,” says Eig. “Doctors were prescribing it, knowing what it really did, and the horse was out of the barn.” Opponents simply couldn't catch up.

Women began using their new freedom to get college degrees, delay marriage and childbearing, and reimagine the balance of power between genders.

“It reinvented what it means to be a woman, what it means to be in a relationship and what it means to be human on this planet, in many fundamental ways," Eig argues. “I don’t think we’d have women on the Supreme Court today without The Pill."

This story first aired as an interview on PRI's Innovation Hub with Kara Miller.