A new Stanford Medicine study reveals that roughly one in 10 people carry genetic variants that make them resistant to GLP-1 receptor agonist medications, even though their bodies produce higher levels of the hormone. This discovery could fundamentally change how doctors decide which diabetes drugs to prescribe, moving toward a more personalized approach based on individual genetics rather than a one-size-fits-all strategy.

GLP-1 receptor agonists, including medications like semaglutide (Ozempic) and liraglutide, have become blockbuster treatments for type 2 diabetes and weight management. More than a quarter of people with type 2 diabetes now take these drugs. However, the new research suggests that for a significant minority of patients, these medications simply don't work as well as expected, even when prescribed at standard doses.

What Is GLP-1 Resistance and Why Does It Matter?

The Stanford team identified a mysterious phenomenon they call "GLP-1 resistance," where people with certain genetic variants have paradoxically higher levels of the hormone GLP-1 (glucagon-like peptide-1) in their bloodstream, but those elevated levels don't translate into better blood sugar control. "Despite people with the PAM variant having higher circulating levels of GLP-1, we saw no evidence of higher biological activity," explained one of the study's senior authors. "More GLP-1 was needed to have the same biological effect, meaning they were resistant to GLP-1".

The genetic variants affect an enzyme called PAM (peptidyl-glycine alpha-amidating monooxygenase), which activates many hormones in the body, including GLP-1. When this enzyme doesn't function properly, it creates a situation where the body produces plenty of GLP-1, but that hormone can't do its job effectively.

In clinical trials, the difference was stark. Among people without the genetic variants, about 25% reached the recommended A1C target (a measure of average blood sugar over three months) after six months of GLP-1 treatment. By contrast, only 11.5% of people with one specific variant and 18.5% with another variant hit that same target. A1C levels are crucial because they reflect long-term blood sugar control and predict risk for diabetes complications.

How Did Researchers Discover This Pattern?

The discovery came from a decade-long international research effort involving experiments in both humans and mice, plus analysis of data from multiple diabetes drug trials. Researchers recruited adult participants and had them drink a sugary solution while measuring their blood every five minutes for four hours. The results surprised them: people with the PAM variants had higher GLP-1 levels than expected, yet their blood sugar didn't improve as much as it should have.

To confirm these unexpected findings, the team collaborated with researchers in Switzerland who were studying mice with the PAM gene removed. Those mice also showed GLP-1 resistance, with elevated hormone levels that didn't help regulate blood sugar. The mice also had faster gastric emptying (food moving through the stomach more quickly), and treating them with GLP-1 medications didn't slow that process down as it normally would.

The researchers still don't fully understand the mechanism behind GLP-1 resistance. "That is the million-dollar question," noted one senior author. "We have ticked off this enormous list of all the ways in which we thought GLP-1 resistance might come about. No matter what we've done, we've not been able to nail precisely why they are resistant".

What Does This Mean for Your Diabetes Treatment?

The practical implication is significant: genetic testing could help doctors identify which patients are likely to respond poorly to GLP-1 medications before they spend months on an ineffective treatment. Currently, doctors often don't know whether a patient will respond well until after six months of treatment, at which point they would need to switch to a different medication. Knowing a patient's genetic makeup upfront could accelerate the path to the right drug.

The study found that people with PAM variants responded normally to other common diabetes medications, including metformin, sulfonylureas, and DPP-4 inhibitors. This specificity is important: the genetic variants only affect how well GLP-1 medications work, not other drug classes. This suggests the resistance is tied specifically to how GLP-1 receptors function in the body.

Interestingly, some longer-acting GLP-1 medications used in pharmaceutical company trials showed similar response rates between people with and without the variants. This hints that higher doses or longer-lasting formulations might overcome the resistance, though more research is needed.

Steps Toward Personalized Diabetes Care

• Genetic Testing: Identifying whether you carry PAM variants could help your doctor predict how well you'll respond to GLP-1 medications before starting treatment, potentially saving months of ineffective therapy.
• Alternative Medication Selection: If genetic testing shows you're likely to be resistant to GLP-1 drugs, your doctor can consider other proven options like metformin, sulfonylureas, or DPP-4 inhibitors that work through different mechanisms.
• Dose Optimization: For people with GLP-1 resistance, higher doses or longer-acting formulations of GLP-1 medications might be more effective, though this requires discussion with your healthcare provider.
• Combination Therapy: Your doctor might combine GLP-1 medications with other diabetes drugs to achieve better blood sugar control if you have the resistant variants.

The research team emphasized that this is just the beginning of precision medicine in diabetes care. "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 one of the study's lead authors. "This is the first step in being able to use someone's genetic make-up to help us improve that decision-making process".

The study was published in April 2026 in Genome Medicine and involved researchers from Stanford, the University of Adelaide in Australia, the University of Parma in Italy, and ETH Zurich in Switzerland. The findings highlight how genetic variation can dramatically influence medication response, even among people with the same diagnosis. As diabetes treatment becomes increasingly personalized, understanding your own genetic profile could be just as important as understanding your blood sugar numbers.