Some people shed pounds fast on GLP-1 drugs like Ozempic or Mounjaro, while others barely budge the scale, and new research says a piece of that gap may be written into your DNA.
Quick Take
- A study of nearly 28,000 people found a gene variant tied to extra weight loss on GLP-1 drugs
- Carriers of one copy lost about 0.76 kg more; two copies meant roughly 1.5 kg more weight loss
- The same gene family was linked to nausea and vomiting, with one side-effect link tied only to tirzepatide users
- Researchers relied on self-reported data from 23andMe customers, not controlled clinical trials
What The New Study Actually Found
Scientists analyzed genetic and treatment data from 27,885 people who reported using GLP-1 receptor agonist drugs, the class that includes semaglutide and tirzepatide. Published in Nature, the study pinpointed a variant in the GLP1R gene, called rs10305420, that showed up far more often in people who lost more weight. The statistical link was strong, with a probability of chance this small that researchers consider it essentially settled science.
The effect scaled with how many copies of the variant a person carried. One copy added about 0.76 kg of extra weight loss over a median of eight months compared to non-carriers. Two copies nearly doubled that gain, adding roughly 1.5 kg. It is not a massive swing, but it is consistent and measurable across a large group of people.
Genes May Also Explain Who Gets Sick From These Drugs
Weight loss was not the only outcome tied to genetics. The research team also found connections between variation in GLP1R and GIPR genes and reports of nausea or vomiting, two of the most common complaints among people taking these medications. Notably, the GIPR link only showed up among people taking tirzepatide, not semaglutide, meaning it cannot be assumed to apply across every drug in this category.
That distinction matters for anyone reading headlines that lump all GLP-1 drugs together. Tirzepatide works on two separate hormone receptors, GLP-1 and GIP, while semaglutide targets only one. A side effect pattern tied to the dual-action drug does not automatically carry over to the single-action one, and conflating the two risks misleading patients and doctors alike.
Why This Study Leaned On 23andMe Customers
To get a sample size this large, researchers used self-reported data from customers of 23andMe, the direct-to-consumer genetic testing company. That approach let them study tens of thousands of people quickly, far more than a typical clinical trial could afford. But it also means the weight loss figures, medication use, and side effects came from what participants reported themselves, not from medical charts or lab measurements.
Self-reported data has real limits. People misremember numbers, round estimates, or skip details when filling out surveys. The 23andMe customer base also skews toward people interested in genetic testing, which may not mirror the broader population of patients prescribed these drugs by doctors for diabetes or obesity. None of that erases the finding, but it does mean the next step is confirming it in formal clinical records.
Putting The Numbers In Perspective
An extra 1.5 kg of weight loss for someone carrying two copies of the gene variant sounds meaningful in a study, but it is small next to the 15 to 20 kg many patients lose on these drugs overall. Genetics appears to explain a slice of why responses differ, not the whole picture. Dose, adherence, diet, baseline weight, and the specific drug prescribed still carry enormous weight in outcomes.
That is consistent with how doctors already think about these medications. Earlier research on older GLP-1 drugs like liraglutide and exenatide found genetic links too, but results bounced around from study to study and never became reliable enough to guide prescribing. This new, much larger study gives researchers a stronger signal to chase, but it is a clue, not a crystal ball.
What Comes Next For Patients And Doctors
Nobody should expect a genetic test to tell them exactly how much weight they will lose on Ozempic or Mounjaro anytime soon. Scientists still need to confirm these results in real clinical trials with verified doses and outcomes, not survey responses. They also need to test whether the gene variant actually changes how the receptor functions in the body, rather than just showing up alongside weight loss by coincidence.
For now, the honest takeaway is that biology partly explains why two people on the same drug and dose can have wildly different results. That is useful knowledge for researchers chasing personalized treatment plans. It is not yet a tool doctors can hand patients. Anyone struggling with side effects or slow progress on these drugs should keep talking to their doctor about dose and drug choice, not wait on a gene test that does not exist yet.
Sources:
reuters.com, nature.com, ddnews.gov.in, thepathologist.com
