More GLP-1 was circulating, but it was accomplishing less.
Among the millions who have turned to GLP-1 medications like Ozempic as a cornerstone of modern diabetes care, roughly one in ten carry a quiet genetic difference that renders these drugs less effective — not through any failure of the medicine itself, but through a deeper biological resistance written into their DNA. Researchers at Stanford Medicine have traced this resistance to variants in genes governing a hormone-activating enzyme called PAM, offering the first molecular explanation for why some patients plateau where others thrive. The discovery opens a door toward precision medicine in diabetes care, where a patient's genetic profile might one day guide treatment before months of trial and uncertainty unfold.
- A paradox at the heart of the research unsettled scientists: patients with a specific PAM gene variant had more GLP-1 circulating in their blood, yet their blood sugar remained stubbornly uncontrolled — more hormone, less effect.
- The culprit is a compromised enzyme called PAM, which normally activates hormones through a process called amidation; without it functioning properly, GLP-1 loses its biological potency before it can do its work.
- Clinicians like endocrinologist Mahesh Umapathysivam describe the daily frustration of watching patients respond wildly differently to the same drug, with no current tool to predict who will benefit and who will be left behind.
- The six-month reassessment window in diabetes care is now in focus — if genetic screening could identify resistant patients early, doctors could redirect treatment faster rather than waiting for failure to become obvious.
- A critical unknown remains: whether this same genetic resistance affects weight loss outcomes, leaving a major question unanswered as Ozempic use surges far beyond the diabetes population.
About one in ten people carry genetic variants that make their bodies resistant to GLP-1 medications like Ozempic, even when the drugs are functioning exactly as designed. Researchers at Stanford Medicine, collaborating with scientists across multiple countries, have identified the source of this resistance in variants affecting an enzyme called PAM, which activates hormones including GLP-1 itself. The findings, published in Genome Medicine, mark the first concrete biological explanation for why a meaningful share of diabetes patients fail to respond adequately to a drug class that has otherwise reshaped treatment for millions.
The discovery emerged from a striking paradox. Participants carrying a PAM variant called p.S539W showed higher circulating levels of GLP-1 than those without it — yet their blood sugar control showed no corresponding benefit. The hormone was present in abundance but had lost its effectiveness. To isolate this genetic effect cleanly, researchers recruited people without diabetes, gave them a sugary drink, and collected blood samples every five minutes over four hours, removing the interference of existing metabolic disease from the data.
The clinical implications center on timing. Diabetes treatment is typically reassessed around the six-month mark, when physicians decide whether to adjust or change medications. Identifying resistant patients through genetic screening before that window could allow doctors to act faster and more precisely — moving toward individualized treatment rather than a one-size-fits-all approach. Study lead Mahesh Umapathysivam, an endocrinologist at the University of Adelaide, described the frustration that motivated the research: the variation in patient response is enormous, and currently there is no reliable way to anticipate it.
What drives the resistance at a molecular level remains, in the words of Stanford geneticist Anna Gloyn, "the million-dollar question." The team has ruled out numerous hypotheses but has not yet identified the precise mechanism. One important boundary also limits the findings: the study addressed blood sugar control only, leaving open whether the same genetic factors affect weight loss — a pressing question as these medications are increasingly prescribed for obesity at higher doses than used in diabetes care.
Roughly one in ten people carry a genetic quirk that makes their bodies resistant to GLP-1 medications like Ozempic, even when the drugs are working as intended. Researchers at Stanford Medicine, working with collaborators across multiple countries, have identified the culprit: variants in genes that control an enzyme called PAM, which activates various hormones including GLP-1 itself. The finding, published in Genome Medicine, offers the first concrete explanation for why some diabetes patients fail to respond adequately to a class of drugs that has otherwise transformed treatment for millions.
The discovery centers on a paradox that initially baffled the research team. When scientists studied adults without diabetes who carried a particular PAM variant called p.S539W, they found something unexpected: these individuals produced higher levels of GLP-1 in their bloodstream than those without the variant. Yet despite this abundance of the hormone, their bodies showed no corresponding improvement in blood sugar control. More GLP-1 was circulating, but it was accomplishing less. The hormone, in other words, had lost its potency.
Anna Gloyn, a pediatrics and genetics professor at Stanford and one of the study's senior authors, described the mechanism with precision: the PAM enzyme performs a chemical process called amidation that extends the lifespan and effectiveness of biologically active peptides. When this enzyme is compromised, multiple systems in the body can malfunction. The researchers zeroed in on two genetic variants that reduce PAM activity, then recruited study participants and gave them a sugary drink while collecting blood samples every five minutes for four hours. By studying people without diabetes, they could isolate the genetic effect from the noise of existing metabolic disease.
What makes this finding clinically significant is timing. Doctors typically reassess a patient's diabetes treatment around the six-month mark, deciding whether to adjust medications or try a different approach. If physicians could identify in advance which patients carry these resistant variants, they could make more informed decisions faster—moving diabetes care closer to what researchers call precision medicine, where treatment is tailored to individual biology rather than applied broadly to all patients. Mahesh Umapathysivam, an endocrinologist and clinical researcher at the University of Adelaide who led the study, noted the frustration that prompted this work: in his clinic, he sees enormous variation in how patients respond to GLP-1 drugs, and there is currently no reliable way to predict who will benefit and who will struggle.
The researchers remain uncertain about the exact mechanism driving GLP-1 resistance in these individuals. Gloyn called it "the million-dollar question." The team has systematically ruled out numerous hypotheses about how the resistance might arise, yet the fundamental cause remains elusive. What is clear is that elevated hormone levels do not translate to improved biological activity—a disconnect that suggests the problem lies not in production but in how the body receives and processes the signal.
One important limitation frames the work: the study focused exclusively on blood sugar control and did not reach firm conclusions about weight loss. Ozempic and its sibling drug Wegovy are prescribed at higher doses for obesity treatment than for diabetes management, and it remains unknown whether the same genetic factors that confer GLP-1 resistance for glucose control also affect weight loss outcomes. Additional research will be needed to answer that question, particularly as these medications have become increasingly popular for weight management beyond the diabetes population.
Citações Notáveis
In some trials, individuals with these variants could not reduce their blood sugar levels as effectively after six months of treatment.— Anna Gloyn, Stanford Medicine
I see enormous variation in how patients respond to these GLP-1 medications, and it is difficult to predict that response clinically. This is the first step toward using a person's genetic makeup to improve our decision-making process.— Mahesh Umapathysivam, University of Adelaide
A Conversa do Hearth Outra perspectiva sobre a história
So these people are making more of the hormone but their bodies aren't responding to it. That seems backwards.
It does. The researchers expected the opposite—that a defective enzyme would mean less GLP-1 in circulation. Instead, the body compensates by producing more, as if trying to overcome the resistance. But more hormone doesn't fix the underlying problem.
Which is what, exactly?
That's the honest answer: they don't know yet. They've ruled out a lot of possibilities, but the mechanism that causes the resistance itself remains a mystery. They can see the effect clearly, but not the cause.
Does this mean Ozempic just won't work for these people, period?
Not necessarily. It means standard doses won't work as well. A doctor might need to use a higher dose, or try a different medication entirely. But knowing who these people are upfront—that's the real value. Right now, doctors waste months finding out someone isn't responding.
And the weight loss question—that's still open?
Completely. These drugs are used at much higher doses for obesity than for diabetes. The genetic resistance they found applies to blood sugar control. Whether it affects weight loss is a separate question that needs its own research.
So this is really just the beginning.
Exactly. It's the first piece of a much larger puzzle about why these drugs work differently in different people.