Danish researchers were examining the use of medications during and after pregnancy when they noticed a clear trend: The number of women using weight-loss drugs like Ozempic and Wegovy soon after childbirth had risen sharply.
In 2018, few women were using the drugs during the first six months after having a baby, with fewer than five prescriptions for every 10,000 new mothers. By mid-2022, that figure had increased to 34 prescriptions for every 10,000 new mothers, and by mid-2024, it had jumped to 173 prescriptions for every 10,000, or almost 2 percent of postpartum mothers. Most of the women were over 30, and two-thirds had more than one child. A majority were overweight, but they did not have diabetes and they had no history of using the drugs, known as GLP-1s, the researchers wrote.
“In a period characterized by natural weight loss and marked hormonal change, this was unexpected,” said Mette Bliddal, a pharmacologist and researcher at University of Southern Denmark in Odense, Denmark, and the paper’s first author.
The new study was published online on Monday in JAMA Network Open.
The analysis examined GLP-1 drug use following 382,277 pregnancies in Denmark from the beginning of 2018 through June 2024. Researchers linked the Danish Medical Birth Register with the country’s National Prescription Registry, enabling them to identify every live birth and every postpartum prescription of a GLP-1 medication.
Although semaglutide, the active ingredient in Wegovy and Ozempic, aids in weight loss, little is known about the drug’s effects after childbirth, when new mothers are experiencing hormonal changes.
Evidence of the drug’s safety for breastfeeding infants is limited: Semaglutide has not been detected in measurable amounts in breast milk and no adverse effects have been seen in breastfed infants of mothers taking it. But very few studies have been carried out, and the long-term effects on a baby’s developing metabolism, pancreas and growth are unknown.
The American College of Obstetricians and Gynecologists has not issued a guidance about the use of weight-loss drugs postpartum because the drugs are so new and the data is insufficient. But First Exposure, a digital information hub and research network at the University of Toronto that provides evidence-based information about drug safety during pregnancy, recommends that patients avoid taking the drugs while breastfeeding. (First Exposure also recommends not taking the medications during pregnancy, and stopping them a month or two before a planned pregnancy).
Even though GLP-1s are not likely to transfer to breast milk in high concentrations and will most likely degrade in the child’s stomach, the organization recommended caution in a 2024 practice article published in the Canadian Medical Association Journal.
“They tend to be large molecules and we know that large molecules don’t transfer efficiently into breast milk,” Dr. Jonathan S. Zipursky, a clinical pharmacologist and toxicologist at the University of Toronto and a medical adviser for First Exposure, said in an interview.
Nevertheless, he said, “I think that out of an abundance of caution, they should not be used in breastfeeding. It’s not because we know there is a safety signal or evidence of harm, but just because we have such poor data that we suggest avoiding it.”
Another concern is that the medications, which suppress appetite, could compromise the production or nutritional quality of breast milk or cause the mother to become dehydrated.
During the postpartum period, “the body is working hard to regain its balance,” Dr. Bliddal said. “We simply do not know how weight-loss medication interacts with those processes or whether it could affect normal physiological recovery.”
There is also no data about how the medication may affect the composition of breast milk, she said. “Even small changes in fat or nutrient content could matter for infant development,” she said.
Roni Caryn Rabin is a Times health reporter focused on maternal and child health, racial and economic disparities in health care, and the influence of money on medicine.
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