“We need to make it affordable and available,” Senator Patty Murray, a Democrat from Washington State and a co-sponsor of the bill, said in an interview in May. “Let’s provide women what they need and make sure it’s affordable so there’s equity, and women who are low-income, women who for whatever reason are struggling don’t have to be forced to not have any birth control simply because they can’t afford it today,” she added.

Opill is known as a “mini pill” because it contains only one hormone, progestin, in contrast to “combination” pills, which contain both progestin and estrogen. A company that makes a combination pill, Cadence Health, has also been in discussions with the F.D.A. about applying for over-the-counter status.

The F.D.A. analysts who evaluated the data Perrigo submitted in its application for a nonprescription Opill had raised concerns about whether women with medical conditions that should preclude them from taking birth control pills — primarily breast cancer and undiagnosed vaginal bleeding — would follow the warnings and avoid the product. The F.D.A. analysts also raised questions about whether younger adolescents and people with limited literacy could follow the directions.

Several advisory committee members said patients with breast cancer, the main medical condition that precludes taking hormonal contraception, typically have doctors who would advise them to avoid birth control pills. They also said that Opill might actually be safest for adolescents because they are very unlikely to have breast cancer. And because young people often start off with contraception they can buy over-the-counter, it is especially important for them to have easy access to a method more effective than condoms and other birth control products available in retail stores, the panelists said.

Perrigo reported that participants in a study took Opill on 92.5 percent of the days they were supposed to take it. Most participants who missed a pill reported that they had followed the label’s directions to take mitigating steps, such as abstaining from sex or using a condom, Dr. Stephanie Sober, the company’s U.S. medical liaison, said at the advisory committee hearing. She said that among 955 participants, only six became pregnant while using Opill.

Most people who said they had missed doses attributed that to running out of pills before they could get to one of the study’s resupply sites, results that, Dr. Sober said, “illustrate precisely the barriers to adherence that could be lessened” by making the pill available over the counter.