GLP-1 receptor agonists like semaglutide and tirzepatide have become some of the most talked about medications in modern medicine, reshaping how millions of people approach weight loss. But a sweeping new study suggests that the results people experience may have less to do with willpower or lifestyle and more to do with what is written in their DNA.
The research, published in the journal Nature, is one of the largest investigations to date into how genetics influence the effectiveness of GLP-1 drugs. Scientists analyzed genetic data and self reported weight-loss outcomes from more than 27,000 people who had used these medications, uncovering two important gene variants that appear to shape both the benefits and the drawbacks of treatment.
The gene variant that gives some patients an extra edge
Researchers identified a specific variation in the GLP-1 receptor gene, known as GLP1R, that functions almost like a built-in performance booster for the drug. People who carry just one copy of this variant lost an average of 1.6 pounds more than those who did not have it.
While that difference may seem modest, scientists say the implications are significant. The findings raise the possibility that genetic testing could one day help doctors better match patients to the medications they are most likely to benefit from an approach known as personalized medicine. Across the full study population, participants lost an average of 24 pounds total, meaning the genetic boost, though real, is one piece of a much larger puzzle.
Still, researchers believe the work represents meaningful progress toward a more tailored approach to obesity treatment.
Why some patients feel far sicker than others
The study also shed light on one of the most common complaints among GLP-1 users: nausea and vomiting. Scientists found a separate gene variant linked to a dramatically higher risk of gastrointestinal side effects and the range was remarkably wide, spanning from 5% to 78% across participants.
Notably, this variant appeared to be drug specific. The GIPR gene variant associated with nausea and vomiting was connected to tirzepatide but not to semaglutide, suggesting that patients who struggle with side effects on one medication might fare better on another.
Importantly, experiencing these side effects did not mean the drug was working less well. Patients with the variant lost just as much weight as those without it they simply felt worse along the way.
What experts say about the study’s limits
Not everyone in the medical community is ready to draw firm conclusions from the data.
A major limitation is that participants reported their own weight rather than having it clinically measured, which introduces the possibility of bias. A comparison sub study that cross-referenced self reported numbers against iPhone health tracking data found a telling gap: users reported an 11.8% weight loss, while the objective electronic data from that same group showed only a 5.8% loss.
The study does not account for key treatment variables like dosing schedules, whether patients stopped taking their medication, or how doses were gradually increased over time. The 23andMe participant pool may not represent the broader, more diverse population of people using these drugs in real world clinical settings.
The research also does not capture serious adverse outcomes such as gastroparesis or pancreatitis, nor does it track longer term clinical markers like diabetes progression. Many of the study’s findings, he added, have not yet been replicated in larger, more rigorously controlled trials.
The bigger picture for patients
Despite these limitations, the study adds important nuance to the growing conversation around GLP-1 medications. Beyond genetics, traditional factors like age, sex and the specific drug being used remain the strongest predictors of how much weight a person will lose. Women in the study saw a higher average body mass index reduction of 12.2%, compared to 10.0% in men.
For patients who have been frustrated by underwhelming results or difficult side effects, the research offers something valuable: a reminder that biology is not one size fits all, and that the future of weightloss treatment may be far more personalized than it is today.
