In recent years, medications such as semaglutide and tirzepatide have transformed the treatment of obesity. These drugs, known as GLP-1–based therapies, have helped millions of adults achieve significant weight loss and improve cardiometabolic health. Yet, as their use has rapidly increased, particularly among women, an urgent question has emerged: Are these medications safe during breastfeeding?
Dr. Gretchen Bandoli from the Center for Better Beginnings at the University of California San Diego is leading a groundbreaking study to help answer that question. With support from a $350,000, three-year Gerber Foundation major research grant, her team is investigating whether antiobesity medications alter the molecular composition of human milk and whether any changes affect infant growth and development.
In the United States, one in three women of reproductive age has obesity, and many experience significant weight retention after pregnancy. While GLP-1 medications offer meaningful health benefits for mothers, there is currently no comprehensive human data guiding their use during lactation. To date, only one study has been conducted, which provided preliminary evidence that GLP-1 medications did not transfer into human milk. However, no additional outcomes, including whether changes occur to macronutrients in the milk, were assessed. Manufacturers report no safety data for breastfeeding infants. As a result, many women are forced to make a difficult choice: delay treatment for their own health or stop breastfeeding earlier than planned.
“Over 50% of medications lack lactation data, resulting in people having to blindly prioritize their own health versus the health of their infants,” said Dr. Bandoli. “Given the well-documented benefit of treating obesity, we are excited to be able to conduct this work to provide meaningful and actionable evidence to individuals who face this difficult decision with extremely little evidence.”
Dr. Bandoli’s study directly addresses this dilemma.
Leveraging UC San Diego’s nationally recognized Human Milk Biorepository, the research team will enroll 60 mother-infant pairs. Forty mothers planning to initiate antiobesity medication will provide milk samples before starting treatment and again at 30 and 60 days after initiation. Twenty similar mothers not using these medications will serve as comparison participants.
Researchers will analyze key components of breast milk, including fats, proteins, lactose, and human milk oligosaccharides (HMOs), using advanced laboratory techniques. These components are known to play critical roles in infant growth, immune protection, and neurodevelopment. The team will also track infant weight gain, health indicators, and early developmental milestones over the first year of life.
The goal is clear: determine whether medication use is associated with measurable changes in milk composition and whether those changes influence early growth or developmental trajectories.
What makes this work especially impactful is its immediate clinical relevance. Historically, it can take more than a decade for lactation safety data to be incorporated into official drug labeling. Dr. Bandoli’s research aims to generate actionable evidence that clinicians and families can use to inform clinical guidance as soon as the research is published.
By funding this important work, The Gerber Foundation continues its commitment to supporting research that enhances the quality of life of infants and young children while recognizing that maternal health and infant health are deeply interconnected.
