10% of Men May Be GLP-1 Resistant — Here's How to Know

What the Stanford Study Actually Found

Published April 10, 2026, in the journal Genome Medicine, the study was a decade-long international collaboration led by Anna Gloyn, DPhil, professor of pediatrics and genetics at Stanford Medicine. The researchers focused on two genetic variants in an enzyme called PAM (peptidyl-glycine alpha-amidating monooxygenase) — the only enzyme in the human body capable of a chemical process called amidation, which activates hormones including GLP-1.

Here's where it gets counterintuitive. The researchers expected that people carrying PAM variants would have lower levels of GLP-1 in their blood. Instead, they found the opposite: carriers had elevated GLP-1 levels, but the hormone was less biologically effective. More GLP-1 was needed to produce the same blood sugar response — the textbook definition of resistance.

The researchers confirmed their findings across multiple experiments — in human participants, in mouse models with the PAM gene knocked out, and in analysis of clinical trial data from 1,119 participants with Type 2 diabetes. The mice lacking the PAM gene showed the same pattern: elevated GLP-1 levels that didn't translate to better blood sugar control.

The Numbers That Matter

When the team analyzed data from three clinical trials of GLP-1 receptor agonists, the results were stark:

That means men carrying the p.S539W variant were roughly half as likely to reach their blood sugar target after six months on a GLP-1 medication compared to non-carriers. And critically, this effect was specific to GLP-1 receptor agonist medications — the same variants had no impact on response to other diabetes drugs like metformin, sulfonylureas, or DPP-4 inhibitors.

What "GLP-1 Resistance" Actually Means

The concept is analogous to insulin resistance, which most men over 40 have at least heard of. With insulin resistance, your body produces insulin, but your cells don't respond to it efficiently. The same basic principle applies here — your body has GLP-1 (or you're taking a medication that mimics it), but the downstream signaling doesn't work as well.

The Stanford team tested every obvious explanation. They checked whether the PAM variants altered GLP-1 receptor expression, receptor binding, or receptor signaling. None of these mechanisms explained the resistance. Whatever is happening occurs further downstream in the biological cascade — and after 10 years of investigation, the researchers still haven't pinpointed exactly where.

"That is the million-dollar question," Gloyn said in the Stanford press release. "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."

The Silver Lining: Longer-Acting Drugs Might Overcome It

There's a critical nuance buried in the data that most coverage of this study missed. Two additional clinical trials — which used longer-acting GLP-1 receptor agonists — showed no significant difference in drug response between carriers and non-carriers. The resistance effect appeared primarily with shorter-acting formulations.

This matters because the most commonly prescribed GLP-1 medications today — semaglutide (Ozempic, Wegovy) and tirzepatide (Mounjaro, Zepbound) — are longer-acting weekly formulations. The older, shorter-acting daily drugs (like liraglutide/Saxenda) may be more affected by GLP-1 resistance.

Gloyn herself noted this possibility, saying researchers might be able to find "formulations of GLP-1, like the longer-acting versions, that avoid the GLP-1 resistance."

Why This Matters More for Men

Three reasons this research hits differently for men:

Men are already less likely to seek treatment. If a man finally overcomes the stigma around weight loss medication, starts a GLP-1, and sees poor results because of an undiagnosed genetic variant, he's far more likely to simply quit than to investigate why it's not working. Understanding that non-response has a biological basis — not a willpower basis — is critical.

Men metabolize these drugs differently. Higher lean body mass, different hormonal profiles, and faster gastric emptying (which GLP-1 medications specifically target) mean the male response to GLP-1s is already more variable. Adding genetic resistance on top of that variability makes personalized prescribing even more important.

The cost equation is brutal. At $149–$399+/month for compounded GLP-1 medications, a man with GLP-1 resistance could spend $1,800–$4,800 over a year on a medication that's working at reduced capacity. Genetic testing that costs a fraction of that could save thousands.

Should You Get Tested?

Right now, there's no commercially available "GLP-1 resistance test" you can order from your doctor. The PAM variants identified in this study are detectable through existing genetic testing platforms, but they aren't yet part of standard pharmacogenomic panels for GLP-1 prescribing.

Here's what you can do today:

If you're considering starting a GLP-1: Ask your provider whether they offer pharmacogenomic testing or can order it. Some telehealth providers are beginning to incorporate genetic data into their prescribing decisions. At minimum, make sure your provider has a clear protocol for non-responders — if you're not seeing results after 8–12 weeks at therapeutic dose, there should be a plan beyond "let's just increase the dose."

If you're already on a GLP-1 and seeing poor results: Don't assume it's your fault. If you've been compliant with medication and haven't seen meaningful weight loss or blood sugar improvement after 3+ months at adequate dosing, bring up the Stanford research with your provider. A medication switch — from a shorter-acting to a longer-acting formulation, or from semaglutide to tirzepatide (which has a dual-agonist mechanism) — may help overcome resistance.

If you've had genetic testing through 23andMe, AncestryDNA, or a clinical panel: Your raw data may already contain information about PAM variants. A genetic counselor can help you interpret whether you carry p.S539W or p.D563G. Note that direct-to-consumer genetic tests vary in their coverage of these specific variants.

What Good Providers Should Be Doing

This research reinforces something we've been saying: the quality of your GLP-1 provider matters. A 2-minute intake quiz and a prescription is not the same as clinical care. Good providers should be:

• Monitoring your response at regular intervals (not just shipping refills)
• Checking metabolic markers beyond just body weight — HbA1c, fasting insulin, lipid panels
• Having a non-responder protocol that goes beyond "increase the dose"
• Staying current on pharmacogenomic research like this Stanford study
• Offering medication switches when first-line treatment isn't working

The Bigger Picture: Precision Medicine Is Coming

Gloyn drew a direct parallel to insulin resistance — a phenomenon that took decades to fully understand but eventually led to an entire class of drugs (insulin sensitizers like metformin and thiazolidinediones) designed specifically to overcome it. The same trajectory is plausible for GLP-1 resistance.

"There are a whole class of medications that are insulin sensitizers," she said, "so perhaps we can develop medications that will allow people to be sensitized to GLP-1s."

For men currently on GLP-1 medications, this isn't a reason to stop treatment. The majority of people — roughly 90% — don't carry these variants. But for the 1 in 10 who do, awareness alone can change the conversation with their provider. The difference between "this drug isn't working, I quit" and "this drug isn't working because of my genetics, let's try something else" is the difference between giving up and getting results.

Endocrinologist Mahesh Umapathysivam, one of the study's lead authors, put it simply: "This is the first step in being able to use someone's genetic make-up to help us improve that decision-making process."

For a population of men who already face barriers to seeking weight loss treatment — stigma, cost, and skepticism — knowing that biology might explain a poor response is the kind of data point that keeps men in the game instead of walking away.