Sixty-six years after the U.S. Food and Drug Administration approved the first oral contraceptive, the small white tablet that became known simply as “the pill” remains a fixture of American life — and a flashpoint. Approved on May 9, 1960, the pill disentangled sex from procreation and gave women the ability to plan their reproductive futures without a partner’s cooperation, a shift that researchers say helped reshape marriage, education and the workforce. “Its introduction in the 1960s afforded U.S. women this unprecedented control over their childbearing and subsequent life trajectories,” said Suzanne Bell, a researcher at the Johns Hopkins Bloomberg School of Public Health.

The pill’s development was spearheaded by birth-control advocate Margaret Sanger, who founded the precursor to Planned Parenthood Federation of America, and funded by her friend and philanthropist Katharine Dexter McCormick. Biologists Gregory Pincus and Min Chueh Chang and OB-GYN Dr. John Rock were instrumental in creating the contraceptive, which uses synthetic progesterone and estrogen to prevent pregnancy — primarily by stopping ovulation, but also by thickening cervical mucus and impeding sperm from entering the uterus. When used perfectly, the pill is 99% effective.

Within two years of initial distribution, more than a million American women were taking it, and monumental social change followed. Researchers have linked the pill to later marriages and greater educational attainment and labor force participation among women. It also played a role in the sexual revolution of the 1960s and ’70s.

The pill spurred backlash almost immediately. In the 1960s, Pope Paul VI condemned it in the encyclical Humanae Vitae, and many states outlawed contraceptives. Although a 1965 U.S. Supreme Court ruling exempted married couples from those bans, prohibitions on use by single women remained in some states for years.

More recently, after the Supreme Court’s decision ending the constitutional right to abortion, some worry that the right to use contraception is also under threat. “With any device or procedure that gives women more reproductive or sexual autonomy, there are always groups that resist and push back,” Bell said, pointing to recent calls for women to have more children.

But on the whole, women are not heeding that message. U.S. fertility rates have reached a historic low, according to the Associated Press, and the pill remains extremely popular. Today it is the most common form of reversible birth control in America, used by more than 8 million people — and still shaping the lives of individuals and the nation, 66 years after its approval.