Cystic fibrosis-related diabetes (CFRD) affects up to 50% of adults with cystic fibrosis (CF) and represents a distinct form of diabetes with features of both type 1 and type 2 diabetes. Unlike typical diabetes, CFRD is driven primarily by progressive pancreatic damage from thick mucus, leading to a gradual decline in insulin secretion. The management of CFRD is uniquely challenging because it requires balancing blood glucose control with the complex nutritional and pulmonary needs of CF. Over the past decade, hormonal therapies—beyond insulin—have gained increasing attention as potential tools to improve outcomes. Understanding the impact of these therapies on CFRD is critical for clinicians, patients, and researchers seeking to preserve lung function, improve nutritional status, and extend survival.

CFRD develops when the same genetic defect that causes the hallmark thick mucus in the lungs also damages the pancreas. The pancreas in CF is progressively destroyed by fibrosis and fatty infiltration, which impairs both exocrine and endocrine function. The loss of beta cells reduces insulin production, while residual beta cells may still secrete some insulin—albeit in an erratic fashion. This creates a unique pattern of glucose intolerance: postprandial hyperglycemia is common, but fasting hyperglycemia appears only later in the disease course.

Diagnosis of CFRD is often delayed because standard diabetes tests can be misleading. Hemoglobin A1c tends to underestimate average blood glucose levels due to increased red blood cell turnover in CF, so the oral glucose tolerance test (OGTT) remains the gold standard. The Cystic Fibrosis Foundation recommends annual OGTT screening for all CF patients aged 10 years and older. Once CFRD develops, it accelerates the decline in lung function and increases the risk of pulmonary exacerbations, making early detection and aggressive management essential.

The impact of CFRD on overall health is profound. Studies show that CF patients with diabetes have significantly lower body mass index (BMI), worse pulmonary function, and increased mortality compared to CF patients without diabetes. Conversely, improved glycemic control in CFRD is associated with better weight maintenance and slowed lung function decline. This bidirectional relationship means that hormonal therapies must be viewed not only as glucose-lowering agents but also as interventions that can positively influence the entire CF disease trajectory.

Role of Hormonal Therapies in CFRD

Hormonal therapies in CFRD center on replacing or enhancing insulin action and other glucoregulatory hormones. While exogenous insulin remains the cornerstone of treatment, a growing body of research explores adjunctive hormonal agents that may offer additional benefits, such as improved insulin secretion, appetite regulation, and even potential anti-inflammatory effects. These therapies target the incretin hormone axis (GLP-1 and GIP) as well as other metabolic pathways. The goal is to achieve glycemic control with fewer injections, reduced hypoglycemia risk, and better overall metabolic health.

Insulin Therapy

Insulin is the only therapy currently approved by the FDA specifically for CFRD, and it is universally recommended for all patients with confirmed CFRD. The rationale is straightforward: CFRD is characterized by absolute or relative insulin deficiency, and insulin replacement directly addresses that deficiency. However, insulin management in CF is far from simple. Patients often require very high doses due to the rapid gastrointestinal transit and malabsorption that accompany CF, and they must coordinate insulin doses with high-calorie, high-fat meals designed to maintain weight.

Rapid-acting insulin analogs—such as lispro, aspart, and glulisine—are the mainstay for prandial coverage. Their fast onset and short duration mimic the normal insulin spike after eating, which is especially helpful because CF patients often have meals that are larger and more frequent than the general population. Long-acting insulin analogs, like insulin glargine or degludec, provide basal coverage and help stabilize overnight and between-meal glucose levels. Some patients with advanced CFRD also require a combination of both. Continuous glucose monitoring (CGM) has become invaluable for guiding insulin dosing and detecting unpredictable fluctuations in blood sugar.

Despite its efficacy, insulin therapy in CFRD carries risks—especially hypoglycemia. CF patients may skip meals due to pulmonary symptoms, or they may have unpredictable absorption of oral nutrition, making insulin doses difficult to adjust. Furthermore, the fear of hypoglycemia often leads to under-dosing and poor glycemic control. Ongoing research into automated insulin delivery systems (closed-loop “artificial pancreas” technology) shows promise for mitigating this risk in CFRD, though large-scale trials are still lacking.

Incretin-Based Therapies

Incretin hormones, particularly glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), are released from the gut after eating and stimulate insulin secretion in a glucose-dependent manner. This property makes them attractive for CFRD, where some beta-cell function may remain, especially early in the disease. Two classes of incretin-based drugs are under investigation: GLP-1 receptor agonists (e.g., liraglutide, semaglutide) and dipeptidyl peptidase-4 (DPP-4) inhibitors (e.g., sitagliptin, saxagliptin).

GLP-1 receptor agonists have shown promise in small studies and case series for CFRD. They enhance glucose-stimulated insulin secretion, slow gastric emptying (which may paradoxically be beneficial in CF by reducing postprandial hyperglycemia), and can promote weight loss. Weight loss is typically desirable in type 2 diabetes, but in CF it is a major concern—most patients struggle to maintain a healthy BMI. However, careful dosing and patient selection might allow GLP-1 agonists to improve glycemic control without causing significant weight loss, especially when used in combination with nutritional support. Additionally, some GLP-1 agonists have anti-inflammatory effects that could theoretically benefit the CF lung. Early clinical data suggest that liraglutide can reduce A1c and improve glucose excursions in CFRD patients, but larger randomized controlled trials are needed.

DPP-4 inhibitors increase endogenous GLP-1 levels by slowing its breakdown. They are oral agents, which is an advantage over injectable GLP-1 agonists. Sitagliptin has been studied in a small crossover trial in CF patients with impaired glucose tolerance, showing a modest improvement in postprandial glucose with a good safety profile. However, DPP-4 inhibitors are generally less potent than GLP-1 agonists and may not be sufficient as monotherapy for established CFRD. Their role may be as an adjunct to insulin or in early-stage disease to preserve beta-cell function.

It is important to note that neither GLP-1 agonists nor DPP-4 inhibitors are currently FDA-approved for CFRD. Their use is considered off-label, and clinicians must weigh potential benefits against risks—particularly gastrointestinal side effects and the possibility of worsening weight loss. Ongoing studies, including those at CF centers, will help clarify their place in the treatment armamentarium.

Other Hormonal and Non-Hormonal Adjunctive Therapies

Beyond insulin and incretins, several other agents have been explored in CFRD, though the evidence base is limited.

SGLT2 inhibitors (e.g., dapagliflozin, empagliflozin) work by increasing urinary glucose excretion independent of insulin. They have revolutionized type 2 diabetes management but are controversial in CFRD because of the risk of volume depletion and ketoacidosis in patients with reduced caloric intake or acute illness. A handful of case reports suggest cautious use in select CFRD patients might be feasible, but larger safety studies are lacking.

Amylin analogs such as pramlintide slow gastric emptying and reduce postprandial glucagon secretion. They are not well-studied in CFRD and may cause nausea—a problematic side effect in a population that already struggles with appetite and nutrition.

Metformin, the cornerstone of type 2 diabetes, is not typically recommended for CFRD because it can cause gastrointestinal distress and lactic acidosis, and its mechanism (improving insulin sensitivity) may not be as relevant in a disease primarily driven by insulin deficiency. However, some centers have used it in patients with mild hyperglycemia and preserved insulin secretion, though this practice is not standard.

Hormonal therapies that address the reproductive axis—such as growth hormone or testosterone—have also been studied for their potential metabolic effects, but data are too sparse to draw conclusions. The role of sex hormones in CFRD is an emerging area, especially as CF patients now live into adulthood and face issues of puberty, fertility, and bone health.

Impact of Hormonal Therapies on Patient Outcomes

The ultimate goal of treating CFRD is not merely to lower blood sugar but to improve overall CF outcomes: lung function, nutritional status, quality of life, and survival. Hormonal therapies directly influence these endpoints through multiple mechanisms.

Lung Function

Poor glycemic control in CFRD accelerates the loss of forced expiratory volume in one second (FEV1), the key measure of pulmonary function. The mechanisms are multifactorial: hyperglycemia impairs neutrophil function, increases airway inflammation, and promotes the growth of pathogenic bacteria like Pseudomonas aeruginosa. Studies have shown that even modest improvements in A1c (e.g., a 1% reduction) are associated with a clinically meaningful slowing of FEV1 decline. Insulin therapy, by providing stable glucose control, has been shown to stabilize or improve lung function in long-term observational cohorts. Emerging hormonal therapies that also have anti-inflammatory properties, such as GLP-1 agonists, have theoretical additional benefits, though human data are not yet available.

Nutritional Status

Maintaining a healthy BMI is a cornerstone of CF care. CFRD often goes hand-in-hand with weight loss, due to both the catabolic state of uncontrolled diabetes and the increased energy demands of frequent infections. Insulin therapy directly promotes anabolism—it facilitates glucose uptake into cells and supports protein synthesis. Many CF patients experience improved appetite and weight gain once they start insulin. Incretin-based therapies, on the other hand, can suppress appetite, which raises caution. However, if used appropriately and combined with aggressive nutritional counseling, some patients may benefit from improved glucose control without net weight loss. The key is individualization.

Quality of Life and Survival

CFRD adds a significant treatment burden to a life already filled with daily airway clearance, enzyme replacement, and frequent clinic visits. Insulin injections, glucose monitoring, and dietary adjustments can contribute to emotional distress and burnout. Hormonal therapies that offer simpler regimens—such as combination insulins or oral agents—could improve adherence and quality of life. Moreover, the survival gap between CF patients with and without diabetes has narrowed in recent decades, largely due to better management of both CF and CFRD. Early and aggressive use of insulin is considered one of the factors behind improved survival in contemporary CF cohorts.

Despite these benefits, there are still many unknowns. The optimal timing of insulin initiation in CFRD remains debated. Some experts advocate starting insulin as soon as any glucose intolerance is detected, even before the formal diagnosis of diabetes, in an attempt to preserve beta-cell function and prevent the vicious cycle of glucotoxicity. Others prefer to wait until hyperglycemia becomes persistent. Similarly, the role of adjunctive hormonal therapies is still evolving, and more research is needed to identify which patients are most likely to benefit from which drugs.

Emerging Therapies and Future Directions

The landscape of CF care has been radically altered by the advent of CFTR modulator therapies, such as elexacaftor/tezacaftor/ivacaftor (Trikafta). These drugs correct the underlying defect in the CFTR protein, leading to dramatic improvements in lung function, sweat chloride levels, and quality of life for many patients. Their impact on CFRD is a topic of intense interest. Early studies suggest that CFTR modulators may improve insulin secretion and glucose tolerance in some patients, possibly by partially restoring pancreatic ductal function and reducing fibrosis. For some individuals, the improvement is enough to delay or even prevent the onset of clinical CFRD. However, not all patients respond equally, and long-term data on diabetes outcomes are still emerging.

Islet cell transplantation has been explored as a treatment for CFRD, but it is currently limited to small, experimental studies. The challenge is that the pancreas in CF is often heavily scarred, making islet isolation difficult. Moreover, patients require lifelong immunosuppression, which poses additional risks for those with chronic lung infections.

Another frontier is the use of inhalable insulin. Because CF patients already have lung damage, inhaling powdered insulin might seem counterintuitive. However, a pressurized inhaler formulation was studied in CFRD and showed non-inferior glycemic control compared to subcutaneous insulin, with no significant adverse pulmonary effects. The convenience of inhaled insulin might improve adherence, but its availability has been limited since the original product was discontinued. Ongoing development of new inhaled insulin formulations could provide a needle-free option for carefully selected patients.

Automated insulin delivery systems (hybrid closed-loop pumps) are rapidly advancing for type 1 diabetes and are now being tested in CFRD. Early pilot studies have shown that these systems can improve time-in-range and reduce hypoglycemia with minimal user intervention. Given the unpredictable nature of CFRD glucose patterns, a closed-loop system could be particularly beneficial. Larger multicenter trials are underway, and it is plausible that such technology will become standard of care for CFRD within the next decade.

Conclusion

Hormonal therapies remain at the core of managing cystic fibrosis-related diabetes, with insulin therapy as the foundation upon which all other interventions are built. The understanding of how these therapies influence CFRD—not only glucose levels but also lung function, nutrition, and quality of life—has deepened substantially. Incretin-based drugs and other emerging hormonal strategies offer hope for more finely tuned treatment regimens that minimize burden and maximize benefit. As CFTR modulators continue to transform the disease and as new technologies like closed-loop systems become more available, the outlook for individuals with CFRD has never been brighter. The next decade will likely see a shift toward personalized, combination hormonal therapies that are tailored to the unique metabolic profile of each patient. For now, a multidisciplinary approach that pairs aggressive hormonal management with nutritional support, exercise, and pulmonary care remains the best path to improving outcomes.

For more detailed information on CFRD management, readers may refer to the Cystic Fibrosis Foundation’s CFRD guidelines. Research summaries on incretin therapies in CF can be found on PubMed, and updates on CFTR modulator effects on glucose metabolism are available through the National Center for Biotechnology Information.