Does overweight affect the effectiveness of the morning after pill? Part of science says yes

In 2011, a team of researchers in Scotland was investigating why the emergency contraceptive pill, popularly known as the morning-after pill, didn’t seem to work for a small portion of the population and made an alarming discovery: the pill failed in higher percentages among women with higher BMI (body mass index).

Since then, several researchers have looked at why and how weight influences the effectiveness of the morning-after pill, but they’ve come across many unknowns: It’s unclear how much less effective it might be for people who are overweight or obese, and there’s no clear research. on how to help someone else solve the problem.

Experts say it is also difficult to define a specific weight at which the effectiveness of the morning-after pill decreases.

“Some studies say there is no effect above a BMI of 25, others say there are some effects — different studies say slightly different things,” said Siripanth Nippita, an associate clinical professor of obstetrics and gynecology at New York University’s Langone Health, in the United States. But in general, she said, as BMI increases, the effectiveness of emergency oral contraceptives decreases.

Part of the reason for this large gap in the general understanding of emergency contraception is because much of the research that led to its creation in the mid-1990s did not initially consider differences in body weight.

“When contraception was first developed, it was really a one-size-fits-all model,” said Alison Edelman, a professor of obstetrics and gynecology at Oregon Health and Science University who has also studied the effectiveness of emergency contraceptives.

“But our population today is very different from when the drugs were developed. We’ve grown in size and fear that the most common type of emergency contraceptive might not work for women with a higher BMI.”

But in general, the morning-after pill greatly reduces the chances of pregnancy. Here’s what we know.

Does the morning after pill have a weight limit?

There are two types of emergency contraceptive pills available in the US: those containing levonorgestrel –also available in Brazil–, and those with ulipristal acetate.

The US Food and Drug Administration (FDA) authorizes these drugs for all women, regardless of weight.

In 2016, the agency said it had completed a review of available research on levonorgestrel contraceptives and found that the data were “conflicting and too limited to draw a definitive conclusion” on whether the pills were less effective in women weighing more than 75 kg or with a BMI greater than 25. BMI uses a person’s height and weight to create a measure of general health. Some doctors consider it a flawed assessment of health.

Studies like the one in Scotland seem to indicate that the morning-after pill may be less effective in women who weigh more than 77 kg, which is the average weight of American women over 20, according to the Centers for Disease Control and Prevention. Illnesses.

“In some studies, we’ve seen some reduction in effectiveness in people with a BMI greater than 25,” said Nisha Verma, a member of the American College of Obstetricians and Gynecologists. “But that doesn’t mean we don’t use it on these people.”

Ulipristal acetate does not have as much of a decrease in effectiveness for women with higher BMIs, she added. But the pill still might not work as well in people who are overweight or obese.

“The evidence is not absolutely clear and consistent,” said David K. Turok, professor of obstetrics and gynecology at the University of Utah.

​Why would a higher BMI make the pill less effective?

Again, the science on this is unclear. Edelman said researchers look at four things when examining a drug’s effectiveness: absorption, distribution, metabolism and excretion. A higher BMI can affect the four processes in different ways.

In individuals with higher BMIs, drugs may be absorbed into the bloodstream at a slower rate, for example, or a drug may end up accumulating fat rather than “working in your favor,” she said.

Monica Woll Rosen, a gynecologist at the University of Michigan School of Medicine, pointed out other potential mechanisms, such as the presence of extra estrogen in the peripheral tissues of overweight people, which can nullify the effects of a contraceptive, or that the dosage might not be strong enough.

Can someone with a high BMI take a higher dose?

Earlier this month, Edelman and his team published a study looking at whether a double dose of the morning-after pill would be effective for someone with a BMI over 30.

They gave 70 women with a BMI greater than 30 a double dose or a single dose of levonorgestrel and monitored them for a week. Unfortunately, the team found no statistically significant difference in ovulation suppression – the main function of the morning-after pill – between the two groups, meaning that a double dose may not be the solution.

In an emergency, however, a double dose of levonorgestrel may be tried. “It’s not unsafe to do that,” Edelman said.

What are the options then?

Doctors recommend ulipristal acetate as a more effective emergency oral contraceptive than levonorgestrel for all women, but especially those with a higher BMI.

You can take the first one for up to five days after unprotected sex. Some doctors recommend having it on hand in case you need to use it. “People must order in advance and suppliers must offer it in advance,” Turok said.

An intrauterine device, if inserted within five days of unprotected intercourse, is an even more effective form of emergency contraception.

The CDC considers the copper IUD, which does not contain hormones, an effective method of emergency contraception, but research shows that hormonal IUDs can also work. These devices act locally in the uterus, Rosen said, meaning “weight shouldn’t make a difference” to their effectiveness. The American College of Obstetricians and Gynecologists also recommends the copper IUD as an alternative to oral contraception for obese women.

Not all women seeking emergency contraception will want a long-term birth control method – the IUD can last three to 12 years. Even for those who want to, the process of getting an appointment in five days and setting aside time for the implantation procedure can be difficult, if not impossible.

“We can spend all day talking about how effective a method is, but if someone can’t access it, it doesn’t work,” said Wing Kay Fok, a gynecologist at Weill Cornell Medicine.

If you can’t take ulipristal acetate or have an IUD inserted, doctors said taking levonorgestrel is still worth it, regardless of your weight or BMI.

An analysis of four WHO (World Health Organization) studies showed that pregnancy rates of women who took the morning-after pill across various BMI categories remained below 3%, indicating that the medication reduces their chances of getting pregnant, although is not a guarantee of preventing pregnancy.

“Better early than late, and something is better than nothing,” Nippita said.

Translated by Luiz Roberto M. Gonçalves