When Caitlyn Pace moved from the United States to Hong Kong three years ago to take a teaching job, she loved the food, the sights and the birth control.

She was was pleasantly surprised to find that in Hong Kong, she could get oral contraceptives at her neighborhood drugstore without a prescription.

"My jaw probably dropped the first time I did it. I just walked in and kind of looked around and was like 'is this really happening?' " said Pace, 34. "It's like buying aspirin."

For years, medical organizations have fought to have over-the-counter birth control pills in the US, too.

On Tuesday and Wednesday, a group of external advisers to the US Food and Drug Administration will discuss an application from a pharmaceutical company to put their prescription birth control pill over-the-counter.

Although professional organizations including the American Medical Association and the American College of Obstetricians and Gynecologists support over-the-counter sales of the drug, called Opill, the FDA seems skeptical, citing a list of concerns in a 130-page document posted online Friday.

"I am worried" about the FDA's decision, said Dr. Kristyn Brandi, a spokesperson for the American College of Obstetricians and Gynecologists.

Concerns about weight, following the label

The FDA scientists say they have two main concerns about Opill, a "mini pill" that uses only the hormone progestin.

One has to do with obesity. The FDA approved Opill as a prescription drug in 1973, and "the prevalence of obesity in adults in the United States has changed dramatically since the original clinical studies were conducted over 50 years ago," the scientists wrote in the document, citing a 13% obesity rate in 1960 compared with a 42% obesity rate now.

"The degree to which efficacy of [Opill] is diminished in individuals who are overweight or obese (which together now represent approximately 60% of the U.S. reproductive-aged population ... ) remains unknown," they added.

The agency cited a 2016 report analyzing data from four studies that suggested women who were obese had an increased risk of pregnancy after taking emergency contraception. The data in those four studies was "limited and poor to fair quality," the authors wrote.

Brandi said she was surprised by the FDA's statements.

In a practice document for its members, the American College of Obstetricians and Gynecologists cites several studies showing that "women with obesity can be offered all hormonal contraceptive method options with reassurance that the efficacy of hormonal contraception is not significantly affected by weight."

Brandi, an obstetrician-gynecologist in New Jersey, noted that even though obesity has been on the rise, there has not been a higher rate of failure for birth control pills.

The FDA scientists were also concerned that studies by Perrigo, the company that manufactures Opill, showed some women didn't follow the label instructions. They said some women in the study didn't take the pill within the same three-hour window every day, which is important for efficacy.

But Brandi said even when doctors prescribe pills, patients don't always take them properly all the time.

"They make mistakes, and we know that," she said. "People are humans, and that's OK."

The Opill label tells women that if they're more than three hours late taking their pill, they should take a pill as soon as they remember and use an additional form of birth control, such as a condom, for two days.

"I trust patients that they'll be able to read the instructions and follow the instructions and be able to use the medication safely and effectively," Brandi said. "I don't worry, because I trust women. I trust my patients."

In a statement, Perrigo said that "data from our eight year development program show that consumers can use Opill safely and effectively as guided by the proposed labelling."

The FDA also expressed concern that without counseling from a doctor, women might not realize when Opill wasn't appropriate for them.

For example, the Opill label states that the drug should not be used by women with a history of breast cancer. But when 205 study subjects with a history of breast cancer read the label, six of them said the pill was right for them.

Women with undiagnosed abnormal vaginal bleeding also are not supposed to use Opill, but in a study, more than half of those with this condition said the pill was appropriate for them.

A letter from lawmakers

The FDA is under pressure to allow Opill to go over-the-counter from elected officials as well as health-care providers.

Unwanted pregnancies are a public health issue in the US, where almost half of all pregnancies are unintended, according to the FDA briefing document, and rates are especially high among lower-income women, Black women and those who haven't completed high school.

In March 2022, 59 members of Congress wrote a letter to FDA Commissioner Dr. Robert Califf about OTC contraception.

"This is a critical issue for reproductive health, rights, and justice. Despite decades of proven safety and effectiveness, people still face immense barriers to getting birth control due to systemic inequities in our healthcare system," the lawmakers wrote.

Califf responded that the FDA "acknowledges the public health benefits of increased access to oral contraceptives" and that "the Agency's decision making is guided by the best available science."

The FDA advisers are expected to vote Wednesday on whether to recommend that the agency approve Opill going over-the-counter. The agency often follows the recommendations of its advisers but doesn't always do so.