Small study finds GLP-1 drugs boost lung function in CF patients
Results suggest treatments are safe; BMI targets may need to be revised
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People with cystic fibrosis (CF) who lost weight while taking GLP-1 receptor agonists (GLP-1 RAs) — medications commonly used for diabetes and weight loss — saw their lung function improve, a small U.S. study found.
While more studies are needed to determine whether these drugs are safe for CF patients, the results suggest guidelines for CF patients’ body mass index (BMI) may need to be “revisited,” the researchers wrote.
Given that higher BMI (a measure of body fat based on weight and height) has historically been associated with better lung function in CF, the findings suggest GLP-1 RA therapy may be safe for weight management even when patients reach a BMI below current CF care guideline targets.
“Future multi-center studies are needed to investigate the efficacy and tolerability of GLP-1 RA therapy in [people with CF]. If these agents are shown to be safe and effective in [people with CF] with normal-range BMI, then current BMI targets in [people with CF] may need to be revisited,” the researchers wrote.
The study, “Impact of glucagon-like-peptide-1 receptor agonist therapy on pulmonary function in people with cystic fibrosis who achieve normal body mass index,” was published in the Journal of Cystic Fibrosis.
New treatments shift thinking on weight
For many years, people with CF were at high risk of malnutrition due in part to poor nutrient absorption, as the thick mucus that builds up in the disease — caused by a defective or absent CFTR protein — can block the pancreas from releasing digestive enzymes into the intestines.
This pattern has shifted with the approval of CFTR modulators, a class of CF treatment that helps boost CFTR protein function in people with certain mutations. As digestion and nutrient uptake improve, more people with CF are gaining excess weight and developing metabolic issues such as diabetes.
As a result, clinicians have begun considering medications widely used for type 2 diabetes and weight loss in the general population, including GLP-1 RAs. These drugs help regulate blood sugar (glucose) and reduce appetite.
But since people with CF have long been encouraged to maintain higher BMI to support lung health, there is “a paucity of evidence regarding the safety and effectiveness of GLP-1 RA therapy” in this population, and whether its use might affect lung function, the researchers noted.
The team analyzed medical records from 13 adults with CF who were treated with GLP-1 RAs at the University of Texas Southwestern Medical Center and the University of Utah CF clinics from October 2019 through March 2025.
Participants ranged in age from 23 to 46, and 12 were women. All but two had pancreatic insufficiency, meaning the pancreas couldn’t release enough digestive enzymes, and all but two also had CF–related diabetes (CFRD).
Ten had been taking Trikafta (elexacaftor/tezacaftor/ivacaftor), one of the approved CFTR modulator therapies in the U.S., since 2020. The median duration of modulator use before starting GLP-1 therapy was 43.4 months, or about 3.5 years.
Seven participants used tirzepatide (marketed in the U.S. as Mounjaro for diabetes and Zepbound for weight loss), and six used injectable semaglutide (sold as Ozempic for diabetes and Wegovy for obesity). They had been using the treatments for three months to 50 months, and most received low doses due to digestive side effects and concerns over excessive weight loss.
Before therapy, the median weight was 71.4 kg (about 157 pounds). After treatment, the median weight was 57.6 kg (approximately 127 pounds), representing a median loss of 11.1 kg (approximately 24.5 pounds) or roughly 15.5% of the initial body weight.
Eleven participants (85%) began treatment with a BMI in the overweight or obese range. After treatment with GLP-1 RAs, all patients reached a BMI within the normal range (18.5 to 24.9 kg/m²), and six ultimately dropped below the current CF guideline targets. Two participants with a normal BMI began therapy to lower their blood sugar levels.
Longer treatment leads to greater improvement
Lung function improved for all patients. All but two participants showed increases in forced expiratory volume in one second (FEV1) — the amount of air exhaled in one second after a forceful breath — and all showed increases in forced vital capacity (FVC), the total amount exhaled after a deep breath. Among those, the median increases were 10.8% for FEV1 and 10.6% for FVC.
“There appeared to be a positive relationship between duration of GLP-1 therapy and improvement in pulmonary function, as patients with longer GLP-1 therapy duration tended to have greater improvement in FEV1,” the researchers wrote.
People treated for 12 months or less had a median FEV1 increase of 6.8%, compared with 17% for those treated longer than 12 months.
Greater reductions in BMI were not linked to greater lung function gains, “suggesting other factors likely contribute … beyond weight loss alone,” the team wrote.
Blood sugar control also improved. Hemoglobin A1c, a marker of long-term glucose levels, dropped by 16.7%.
The researchers noted that better glucose control, combined with improved breathing mechanics resulting from weight loss, may have contributed to the improvements in lung function.
They also noted that GLP-1 receptors are found in lung tissue, and experimental studies suggest they may influence the production of surfactant, a slippery substance that helps keep the air sacs open so breathing is easier, as well as the function of pulmonary artery smooth muscle.
“Overall, these findings suggest that GLP-1 RA therapy may improve lung function through overlapping pathways and complement the benefits of CFTR modulators,” the team concluded.
