1 in 10 People May Be Resistant to GLP-1 Drugs: The Stanford Discovery That Could Save You Thousands

Stanford researchers discovered that approximately 10% of the population carries genetic variants that make GLP-1 medications significantly less effective — a finding that could reshape how these drugs are prescribed.

The Variant That Changes Everything

In April 2026, a team of researchers led by Dr. Anna Gloyn at Stanford Medicine published findings that could fundamentally change how GLP-1 medications are prescribed. Their discovery: approximately 10% of the general population carries genetic variants in a gene called PAM (peptidylglycine alpha-amidating monooxygenase) that make GLP-1 drugs measurably less effective.

Not slightly less effective. Measurably, mechanistically less effective — with implications for appetite suppression, gastric emptying, and weight loss outcomes.

What PAM Does (and What Happens When It's Broken)

The PAM gene encodes an enzyme that performs a critical final modification (called amidation) to many hormones in the body, including GLP-1 itself. Without proper amidation, GLP-1 is produced in normal or even elevated quantities — but it doesn't work as well.

The researchers studied a specific PAM variant called p.S539W. Here's what they found when they recruited participants with and without the variant, gave them a sugary drink, and measured their blood every five minutes for four hours:

This is a paradox: people with the PAM variant have more GLP-1 circulating in their blood, but it's less biologically potent. The researchers call this phenomenon GLP-1 resistance — a concept that's completely new to endocrinology.

The Mouse Studies Confirmed the Mechanism

To verify the mechanism, the team studied mice lacking the PAM gene entirely. These mice had faster gastric emptying (the opposite of what GLP-1 drugs are supposed to do). When the researchers administered a GLP-1 receptor agonist, it failed to slow gastric emptying in these mice — while working normally in control animals.

Importantly, the problem isn't with the GLP-1 receptors themselves. Working with collaborators in Copenhagen, the team demonstrated that PAM deficiency doesn't alter the receptor's ability to bind GLP-1 or how the hormone signals through the receptor. The issue is upstream: the hormone itself is structurally modified in a way that reduces its effectiveness, even though the body makes plenty of it.

What This Means for the 30+ Million People on GLP-1s

If you've been on a GLP-1 medication for several months and the results have been disappointing — minimal appetite suppression, less weight loss than expected, no real change in "food noise" — you may not be doing anything wrong. You may be among the roughly 1 in 10 people whose genetics make the medication inherently less effective for you.

Pharmacogenomic testing for PAM variants is not yet standard clinical practice — but this study makes a strong case that it should be. If GLP-1s are going to be prescribed to tens of millions of people, identifying the 10% who won't respond well before they spend months on an ineffective (and expensive) medication is both clinically and economically sensible.