In the year when GLP-1 drugs have become the centerpiece of American diabetes and obesity treatment, when Medicare is preparing to launch a $50/month Wegovy copay program on July 1, when the oral Wegovy pill has generated 1.3 million prescriptions in its first quarter, and when a Penn Medicine study just confirmed a 30% breast cancer risk reduction for women on these drugs, a Stanford Medicine study published Genome Medicine in April 2026 and surfacing widely in medical news this week reveals a finding that every patient, every prescribing physician, and every insurer building GLP-1 formulary strategies needs to understand.
The study finds that approximately 10% of the general population carries genetic variants that make them significantly less responsive to GLP-1 receptor agonists. For these individuals, estimated at roughly 33 million Americans, drugs such as Ozempic, Wegovy, Mounjaro, and Zepbound may not work as expected for blood sugar control, regardless of dose or adherence. Researchers also note that regions with high diabetes burden may have large numbers of these non-responders who have not yet been identified.
For San Antonio, where 17% of Bexar County adults have diagnosed Type 2 diabetes and where GLP-1 drugs are increasingly described by physicians as "revolutionary," and for Dallas, where childhood Type 2 diabetes is rising, and UT Southwestern's Simmons Cancer Center is a major center for metabolic research, the Stanford findings carry direct clinical relevance.
It is a clinical reality that changes how physicians should be prescribing and monitoring the most in-demand drug class in American medicine. "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 endocrinologist Mahesh Umapathysivam of Adelaide University, a study collaborator.
The Science: What the PAM Gene Variant Does
The molecular mechanism behind GLP-1 resistance centers on an enzyme called PAM, or peptidyl-glycine alpha-amidating monooxygenase. PAM helps activate certain peptide hormones, including GLP-1. When it does not function properly, these hormones are still produced, but they are not fully activated. As a result, they can circulate in the blood at normal or even higher levels, but they do not signal the body as effectively as they should.
In people with PAM gene variants, specifically p.S539W and p.D563G, circulating GLP-1 levels are actually higher than normal — but the hormone is less biologically effective. This means the body requires more GLP-1 activity to achieve the same effects, including insulin release, slower digestion, and reduced appetite. When GLP-1 receptor agonist drugs are used, they also produce a weaker response in these individuals because the underlying signaling pathway is less responsive.
Researchers supported these findings through multiple lines of evidence. In mouse models where the PAM gene was disabled, animals developed GLP-1 resistance. In human participants with the p.S539W variant, blood sugar levels declined more slowly after a glucose challenge. And in a pooled analysis of 1,119 participants from GLP-1 drug trials, carriers of PAM variants showed lower rates of meaningful blood sugar control compared with non-carriers.
Who Carries These Variants — and Why Diabetes Cities Need to Know
PAM variants are present in roughly 10% of the general population, but they are more common in people with Type 2 diabetes than in the general population. The biological explanation is significant: PAM variants reduce GLP-1 activation, meaning the body's natural ability to regulate blood sugar after meals is already partly impaired before diabetes is diagnosed. This suggests the variant is not only linked to drug response but may also contribute to diabetes risk itself.
In regions with high diabetes prevalence, including San Antonio, Houston, and the broader Texas Diabetes Belt across Bexar, Hidalgo, and Webb counties, the share of patients with PAM variants among those with diabetes may be higher than the general estimate of 10%. This becomes especially important as July 1 approaches and large numbers of Medicare patients begin Wegovy under the Bridge program.
The practical implication is that a patient who starts Wegovy, takes it consistently for three to six months, and does not see expected improvements in blood sugar or weight should not automatically be viewed as non-adherent or facing behavioral challenges. They may instead fall within the estimated 10% of individuals with PAM variants for whom GLP-1 drugs are biologically less effective. The Stanford study suggests that testing for PAM variants could help identify these patients earlier and guide physicians toward alternative treatments, such as SGLT2 inhibitors, higher-dose tirzepatide combinations, or other drug classes, rather than continuing ineffective therapy for extended periods.
What This Means for San Antonio's Texas Diabetes Institute and UT Southwestern
The Texas Diabetes Institute at University Health, described as a leading diabetes care and research center in the United States, along with diabetes research programs at UT Southwestern Medical Center, are positioned to play a key role in translating the PAM variant discovery into clinical practice. Precision medicine in diabetes, which matches patients to medications based on genetic and metabolic profiles rather than using the same drug class for everyone with Type 2 diabetes, is increasingly seen as the next frontier in treatment. The Stanford PAM research is among the most important recent contributions to that shift.
For patients currently taking GLP-1 medications who are not achieving expected results, the Stanford researchers note that the underlying mechanism behind GLP-1 resistance is still not fully understood, and that weight loss specifically has not yet been characterized in this study. The current evidence focuses on blood sugar regulation. Patients experiencing poor glucose control on these drugs are encouraged to speak with their endocrinologist or primary care provider about the possibility of PAM variant status.
Genetic testing for PAM variants is not yet part of standard clinical care, but it is becoming more accessible as pharmacogenomic testing expands. Several major health systems, including UT Southwestern, already offer pharmacogenomic panels, and researchers expect PAM to be incorporated into broader diabetes precision medicine testing in the next few years.
The Bigger Precision Medicine Picture
The GLP-1 resistance discovery is part of a broader scientific revolution in diabetes care that is moving from population-level treatment protocols toward genetically and metabolically personalized medicine. The American Diabetes Association's 2026 Standards of Care already acknowledge that individual patient response to GLP-1 therapy varies substantially — they simply have not had a molecular explanation for much of that variation until now. The Stanford PAM study provides the first clear genetic mechanism for a significant fraction of GLP-1 non-responders. Its publication this spring, followed by its wider clinical dissemination this week as physicians prepare for the July 1 Medicare GLP-1 Bridge launch, could not be better timed. The 10% of patients carrying PAM variants deserve prescribers who know they exist — and in San Antonio, where the stakes of getting diabetes treatment right are higher than almost anywhere in America, that knowledge is now available.
