Women on birth control are more likely to later take semaglutide than those who never start contraceptives, according to a recent study in JAMA Network Open.

The study using Danish national registries also found that women with a low or normal BMI who used any type of contraceptive were generally more likely than those with overweight or obesity to initiate semaglutide.

Despite being “a very common, widely used drug in a very large population that’s prescribed to young and healthy women in very important stages of life,” existing research on the association between hormonal contraceptives and weight gain is mixed, said Mille Dybdal Bager, MD, a researcher at Steno Diabetes Center Copenhagen in Herlev, Denmark, who led the study.

Most studies have found no or very modest associations with weight gain, but many patients report it as a side effect.

Kathryn Thomas, MD, assistant professor of ob/gyn at WashU Medicine in St. Louis, said the research highlights a need for more studies on the association between birth control and weight gain “in different subsets of people with different risk factors. This will help inform clinicians and patients more about options, side effects, and what to look out for. There is a lot that we do not know.” 

About 22% of US women aged between 15 and 49 years use hormonal contraceptives, whereas an estimated 11% of adults reported using a GLP-1 medication in 2026. Women aged between 30 and 49 years are twice as likely as men to have used a GLP-1.

The case-control study included data of 249,643 women aged between 15 and 49 years (average age, 37 years) included in multiple Danish registries from 1996 to 2023. A little over 9% were on semaglutide (Ozempic or Wegovy), and the remainder had never taken the drug, comprising the matched control group. Almost half of the semaglutide users and less than one ninth of women in the control group had obesity.

Women who had started using semaglutide prior to a form of hormonal birth control were excluded from the study, as were women with preexisting conditions, such as polyendocrine metabolic ovarian syndrome, formerly known as polycystic ovary syndrome, or who were on menopausal hormone therapy.

Dybdal Bager and colleagues looked backward from the date of first semaglutide prescription to analyze hormonal contraception utilization.

Nearly three quarters of those who had taken contraceptives only used one method, whereas the remainder had switched three or more times or had used less common methods such as an implant or ring.

Overall, the more times a woman switched birth control methods, the more likely they were to initiate semaglutide. Women who switched more than three times were more than twice as likely as those who did not use hormonal contraceptives to start semaglutide (hazard ratio [HR], 2.31; 95% CI, 2.06-2.58) after adjusting for BMI.

Researchers cautioned, however, that correlation does not equal causation, and as women age, they may be more likely to try new methods of contraception and seek solutions for age-related weight gain.

When broken out by weight, women with a BMI less than 25 who switched their birth control method more than three times were nearly 3.71 times as likely as those in the same range who did use contraceptives to start semaglutide (95% CI, 2.84-4.85).

“It could be because [these women] have different health-seeking behaviors or go to the doctor more often and maybe they are a person who is not afraid of using medical treatments, and then they’re more likely to initiate semaglutide later in life than a person who doesn’t like using medical drugs,” said Dybdal Bager said.

Those with a normal or low BMI who exclusively used a progestin-only intrauterine device had a stronger likelihood of semaglutide use than never users with the same weight range (HR, 2.14; 95% CI, 1.43-3.2).

The only group not associated with statistically significant use of semaglutide was women with a normal or low BMI who exclusively used the progestin-only pill (HR, 1.08; 95% CI, 0.56-2.11).

Evidence shows most birth control methods, aside from the Depo-Provera shot, do not cause clinically significant weight gain, Thomas said.

“However, perceived weight gain is a known common cause of stopping a birth control method, so this is an important worry for many people,” Thomas said. “It’s so important for providers to listen to these concerns when patients report them so that they can find a method that meets all of their needs.” 

If a patient wants to switch contraceptives, clinicians address any weight concerns, Dybdal Bager said. Although she said GLP-1s can be a useful tool, they should not replace a healthy diet and exercise.

This study was funded by the Novo Nordisk Foundation. Dybdal Bager and Thomas reported no financial conflicts of interest.

Kelsey Mesmer, PhD, is a freelance journalist and journalism professor at Saint Louis University in St. Louis.