Genetic Variants May Reduce GLP-1 Diabetes Drug Effectiveness

More than a quarter of people with Type 2 diabetes take GLP-1 receptor agonists, popular medications like Ozempic and Wegovy that mimic the hormone glucagon-like peptide-1 (GLP-1) to regulate blood sugar. However, a groundbreaking study from Stanford Medicine scientists reveals that genetic variants carried by roughly 10% of the general population may cause GLP-1 resistance, making these drugs less effective for blood sugar control in affected individuals.

Published on March 29, 2026, in Genome Medicine (DOI: 10.1186/s13073-026-01630-0), this decadelong international effort combined human experiments, mouse models, and analysis of diabetes drug trial data. The findings highlight a path toward precision medicine, helping doctors identify non-responders early and adjust treatments accordingly.

What Are GLP-1 Receptor Agonists and How Do They Work?

GLP-1 receptor agonists are injectable medications that imitate the natural gut hormone GLP-1, which is released after meals. This hormone plays a crucial role in metabolic health by:

• Stimulating insulin release from the pancreas to lower blood sugar.
• Slowing gastric emptying to prevent post-meal glucose spikes.
• Reducing appetite, aiding weight management.

For Type 2 diabetes, these drugs improve glycemic control, often measured by HbA1c levels. At higher doses, drugs like Ozempic (semaglutide) and Wegovy are prescribed for obesity. Despite their popularity, response varies widely among patients, prompting researchers to investigate genetic factors.

Discovering GLP-1 Resistance: The Role of PAM Genetic Variants

The study pinpointed two genetic variants in the gene for peptidyl-glycine alpha-amidating monooxygenase (PAM), an enzyme essential for activating hormones like GLP-1 through a process called amidation. This chemical modification increases the half-life and potency of peptides.

"PAM is a truly fascinating enzyme because it's the only enzyme we have that's capable of a chemical process called amidation, which increases the half-life or the potency of biologically active peptides," said Anna Gloyn, DPhil, professor of pediatrics and of genetics at Stanford Medicine and one of the study's senior authors.

PAM variants, such as p.S539W and p.D563G, are more common in people with diabetes and were previously linked to impaired insulin release. Researchers hypothesized they might also disrupt GLP-1 function, leading to unexpected results.

Human Experiments Reveal Surprising Findings

Adult participants with and without the p.S539W PAM variant (without diabetes to minimize variables) drank a sugary solution, with blood measured every five minutes for four hours. Contrary to expectations of lower GLP-1 levels, carriers had higher circulating GLP-1 levels but no enhanced biological activity—no faster blood sugar reduction.

"Despite people with the PAM variant having higher circulating levels of GLP-1, we saw no evidence of higher biological activity. They were not reducing their blood sugar levels more quickly. More GLP-1 was needed to have the same biological effect, meaning they were resistant to GLP-1," Gloyn explained.

Confirmation in Mouse Models

Collaborators in Zurich studied mice with the PAM gene knocked out, which mirrored human GLP-1 resistance: elevated GLP-1 without blood sugar benefits. These mice showed faster gastric emptying, unresponsive to GLP-1 agonists. Pancreatic and gut tissues displayed reduced GLP-1 response, despite unchanged receptor expression.

Further work with Copenhagen researchers confirmed intact GLP-1 binding and signaling at receptors, suggesting resistance occurs downstream.

Clinical Trial Data: Real-World Impact on Treatment Response

A meta-analysis of three trials involving 1,119 Type 2 diabetes participants showed carriers of PAM variants were less responsive to GLP-1 receptor agonists. After six months:

• About 25% of non-carriers reached recommended HbA1c targets.
• Only 11.5% with p.S539W and 18.5% with p.D563G did.

"In some of the trials, we saw that individuals who had those variants were unable to lower their blood glucose levels as effectively after six months of treatment," Gloyn noted.

Strikingly, responses to other diabetes drugs like sulfonylureas, metformin, and DPP-4 inhibitors were unaffected.

"What was really striking was that we saw no effect from whether you have a variant on your response to other types of diabetes medications," Gloyn said. "We can see very clearly that this is specific to medications that are working through GLP-1 receptor pharmacology."

Two pharma-funded trials with longer-acting GLP-1 agonists showed similar responses between groups, hinting that formulation differences might overcome resistance.

Implications for Weight Loss and Obesity Treatment

The study focused on blood sugar but noted uncertainty for weight loss, as Ozempic and Wegovy use higher doses for obesity. Limited weight data from two trials showed no differences, but more research is needed. Gloyn emphasized that pharma companies often collect genetic data, which could clarify genetic influences on weight loss responders.

Why Does GLP-1 Resistance Happen? The Unresolved Mechanism

Despite exhaustive testing, the exact cause remains elusive—described as "the million-dollar question" by Gloyn. They've ruled out many possibilities, likening it to insulin resistance, which is multifactorial yet treatable.

"There are a whole class of medications that are insulin sensitizers, so perhaps we can develop medications that will allow people to be sensitized to GLP-1s or find formulations of GLP-1, like the longer-acting versions, that avoid the GLP-1 resistance," she said.

What This Means for Patients with Type 2 Diabetes

Genetic testing for PAM variants could enable precision medicine, predicting poor responders and prompting earlier switches—potentially avoiding months of suboptimal treatment.

"When I treat patients in the diabetes clinic, I see a huge variation in response to these GLP-1-based medications and it is difficult to predict this response clinically," said lead author Mahesh Umapathysivam, MBBS, DPhil. "This is the first step in being able to use someone's genetic make-up to help us improve that decision-making process."

Patients should discuss genetic factors with their endocrinologist, especially if HbA1c doesn't improve after 3-6 months on GLP-1 therapy. Tools like Shotlee can help track symptoms, blood sugar trends, and side effects to inform discussions. Common side effects of GLP-1s include nausea and gastrointestinal issues, but genetic resistance adds another layer—monitoring is key.

Compared to alternatives like metformin (first-line, oral, weight-neutral) or SGLT2 inhibitors (cardioprotective), GLP-1s excel in weight loss but may not suit everyone genetically.

Key Takeaways

• PAM variants (p.S539W, p.D563G) in ~10% of people cause GLP-1 resistance: higher GLP-1 levels, poorer blood sugar response.
• Affects GLP-1 agonists specifically; no impact on metformin, sulfonylureas, or DPP-4i.
• Meta-analysis: Fewer variant carriers hit HbA1c targets (11.5-18.5% vs. 25%).
• Longer-acting formulations may bypass resistance.
• Future: Genetic testing for personalized Type 2 diabetes care.

Conclusion: Toward Precision Metabolic Health

This Stanford-led study, involving experts like Markus Stoffel, MD, PhD, and contributors from Oxford, Dundee, and more, funded by Wellcome, NIH, and others, opens doors to tailored GLP-1 therapy. Patients and providers can now consider genetics in metabolic health strategies, optimizing outcomes for Type 2 diabetes and beyond. Stay informed on emerging research to make data-driven decisions.