Effects of GLP-1 RAs on Human Lactation Outcomes

There is increasing interest in using GLP-1 Receptor Agonist (GLP-1 RA) medications after pregnancy. This study is designed to determine if these medications affect breastmilk production or the nutritional makeup of breastmilk.

The main questions the study will address are:

• Does GLP-1 RA-induced weight loss increase or decrease breastmilk production?
• Does GLP-1 RA-induced weight loss affect the nutritional composition of milk, including milk fat content?

Researchers will assess milk production rates before and after mothers begin taking injected GLP-1 RA medications to decrease their body weight. Weight loss will be confirmed with 7-day body weight averages.

Participants will:

• Weigh themselves and report measurements daily.
• Participate in 2-3 morning study visits over approx. 2.5-4.5 months (approx. 3-3.5hrs each).

During each visit, participants will:

• Use a study provided breastpump to express milk 3 times hourly for measurement of hourly milk production.
• Provide 1-3 oz of milk for further study.
• Answer questions about breastfeeding patterns.

Study Overview

• Status: Recruiting
• Conditions: Weight Loss; Lactation
• Intervention / Treatment: Drug: Injected GLP-1 Receptor Agonists and Dual Agonists

• Study Type: Observational
• Enrollment (Estimated): 18

Contacts and Locations

• Study Contact: Name: Jayne F Martin Carli, PhD; Phone Number: 303-724-3981; Email: jayne.martincarli@cuanschutz.edu
• Study Contact Backup: Name: Jacinda M Nicklas, MD, MPH; Phone Number: 303-724-9028; Email: jacinda.nicklas@cuanschutz.edu

Study Locations

• United States
  • Colorado
    • Aurora, Colorado, United States, 80045
      • Recruiting
      • University of Colorado Anschutz School of Medicine

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Child; Adult; Older Adult
• Accepts Healthy Volunteers: Yes

• Sampling Method: Non-Probability Sample

Study Population

Breastfeeding mothers willing to attend study study visits in Aurora, CO.

Description

Inclusion Criteria:

• Breastfeeding mothers of single or multiple infants.
• Milk removal at least 4x daily
• Eligible for a GLP-1 RA administered subcutaneously (oral GLP-1 RAs contain absorption enhancers, which may drive accumulation in milk)
• Access to a breastpump, if needed for maintaining breastfeeding behaviors.
• Willingness to provide 1-3 oz of breastmilk per study visit.
• Willingness to track and report body weight daily.
• Willingness to maintain breastfeeding behaviors for the duration of the study.

Exclusion Criteria:

• Currently taking GLP-1 RA medication or other weight loss medication
• Induced lactation, due to unknowns regarding the durability of the mammary gland's milk production after exogenous stimulation.

Study Plan

How is the study designed?

Number of groups / cohorts

1

Cohorts and Interventions

Group / Cohort

Intervention / Treatment

Breastfeeding mothers prescribed GLP-1 RA therapies; Breastfeeding mothers who have been prescribed, but have not started, an injected GLP-1RA (these patients have an indication for GLP-1 RA treatment (BMI ≥27 kg/m2 with at least one comorbidity (prediabetes, diabetes, metabolic syndrome, obstructive sleep apnea, hypertension, dyslipidemia, cardiovascular disease, heart failure, chronic kidney disease, metabolic dysfunction-associated steatohepatitis, atrial fibrillation, venous thromboembolic disease, osteoarthritis, polyendocrine metabolic ovarian syndrome), or BMI ≥30 kg/m2)) and who are committed to sustaining breastfeeding habits (frequency and volume of milk removal) for the duration of the study period.

Drug: Injected GLP-1 Receptor Agonists and Dual Agonists; Participants are prescribed this medication by their care provider(s) as part of their postnatal clinical care, including but not limited to semaglutide and tirzepatide. The investigators do not provide, manage, or assign the medication.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Hourly milk production rate	Milk production rate (in grams per hour) will be assessed using a standardized milk expression protocol.	From one week before until a maximum of 2 months after beginning GLP-1RA treatment. This timeframe will restart if their dosage is increased.
Milk macronutrient composition	Milk macronutrient composition will be assessed using the Miris Human Milk Analyzer.	From one week before until a maximum of 2 months after beginning GLP-1RA treatment. This timeframe will restart if the dosage is increased.

Collaborators and Investigators

• Sponsor: University of Colorado, Denver

Study record dates

Study Major Dates

• Study Start (Estimated): July 1, 2026
• Primary Completion (Estimated): June 1, 2028
• Study Completion (Estimated): June 1, 2028

Study Registration Dates

• First Submitted: July 17, 2026
• First Submitted That Met QC Criteria: July 17, 2026
• First Posted (Actual): July 22, 2026

Study Record Updates

• Last Update Posted (Actual): July 22, 2026
• Last Update Submitted That Met QC Criteria: July 17, 2026
• Last Verified: July 1, 2026

More Information

Terms related to this study

• Keywords: GLP-1; Weight Loss; Breastmilk production; Breastmilk composition
• Additional Relevant MeSH Terms: Body Weight; Body Weight Changes; Pathological Conditions, Signs and Symptoms; Behavior; Signs and Symptoms; Feeding Behavior; Weight Loss; Breast Feeding
• Other Study ID Numbers: 26-1234

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: YES
• IPD Plan Description: De-identified individual participant data and leftover biological samples may be deposited into public or restricted-access data banks, or distributed directly to external researchers for future study without additional participant consent. Data and specimens will be stripped of names and direct identifiers prior to sharing or repository submission. Recipients of these assets may include researchers working at other universities, government agencies, or private industry. Future research utilizing this data may focus on obesity, weight loss treatments, or other related medical conditions. While data are de-identified to protect privacy, absolute protection against re-identification cannot be guaranteed, and broad data sharing may involve unknown risks.
• IPD Sharing Time Frame: Data will be made available following the primary completion of the study and publication of main results, or upon deposition into designated data repositories.
• IPD Sharing Access Criteria: Data and leftover samples will be accessible to qualified researchers across academic, government, and private industry sectors. Access to data housed in restricted data banks will be governed by the specific repository's data access committee. Direct requests to the study investigators will require a scientifically valid proposal.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: Yes
• Studies a U.S. FDA-regulated device product: No
• product manufactured in and exported from the U.S.: No