If you have started semaglutide (Ozempic, Wegovy) or tirzepatide (Mounjaro, Zepbound) and found that your results look different from someone else's on the same dose, you are not imagining it. A large genetic study published in Nature in April 2026 by researchers at the 23andMe Research Institute set out to explain some of that variation. Here is what the study actually found, and just as importantly, what it does not mean for your own treatment.
What the researchers found
The study looked at nearly 28,000 people who had taken a GLP-1 medication, searching for genetic variants linked to weight loss and to side effects such as nausea and vomiting. Two results stood out.
GLP1R. This is the gene that codes for the receptor these medications work on. People carrying a particular variant of this gene lost, on average, an extra 0.76 kg per copy of the variant. The same region was also tied to a higher likelihood of nausea, echoing a broader pattern in the data: people who feel more nauseous on treatment tend to lose somewhat more weight.
GIPR. This variant was linked to vomiting, but only in people taking tirzepatide. That distinction makes sense biologically. Semaglutide targets a single hormone receptor (GLP-1), while tirzepatide targets two (GLP-1 and GIP). The GIPR variant affects the GIP side of things, which is presumably why its effect only turned up in tirzepatide users and not semaglutide users.
Both findings come from a peer-reviewed study, and the GLP1R result was independently checked against a second dataset (All of Us) using medical records rather than self-reported outcomes. That is a stronger form of evidence than a single self-report survey.
Why genetics is only a small part of the story
It would be easy to read the headlines and assume genetics now explains why treatment works better for some people than others. The study itself does not support that conclusion.
When the researchers combined clinical, demographic and genetic information into one model, it accounted for around a quarter of the variation seen in weight loss outcomes, and genetics made up only a small fraction of that quarter. The bigger drivers of outcome were:
Which medication was used (tirzepatide showed greater median weight loss than semaglutide in this cohort)
Sex (women lost somewhat more weight on average than men)
Existing conditions such as type 2 diabetes, high blood pressure and fatty liver disease, each associated with somewhat reduced efficacy
Dose and how long someone had been on treatment
So the honest summary of this research is "some genes appear to play a role," not "genetics explains why your results differ from someone else's." Those are two very different claims.
Can you get a genetic test to find your right dose?
Not currently, and not in the UK. The study's own authors describe this as an early step towards more personalised prescribing, not a finished clinical tool. A commercial report based on these findings has been launched in the US, but it is only available through a physician-supervised service and is designed to be interpreted alongside a clinician, not read on its own. There is no equivalent test built into NHS or UK private prescribing pathways for GLP-1 medications.
What decides your dose and monitoring today is what has always decided it: your medical history, your current health, how you respond as treatment progresses, and the judgement of your prescriber. That is not an outdated approach waiting to be replaced by a DNA test. It is simply the current evidence-based standard.
If your results feel different to someone else's
This is probably the most useful takeaway from the research. It adds solid evidence that differences in response to the same medication at the same dose are, at least in part, biological rather than a question of effort. Some of that is genetic. A larger share comes down to sex, existing health conditions, and clinical factors like dose and duration.
If your progress does not match what you expected, or what you have seen from someone else's experience, that is not a personal failing, and a genetic test would not meaningfully explain it away either. It is a reason to speak with your prescriber about how your treatment is going, rather than a reason to look for answers on your own.
What this means for you
This research is a genuinely interesting step in understanding why GLP-1 medications affect people differently, and there will likely be more to come. For now, though, genetics is one contributing factor among several, it is not something you can currently test for as part of UK clinical practice, and it does not change what determines a safe and effective treatment plan: proper assessment, the right dose for you, and an ongoing conversation with your prescriber.
If you have any questions about your treatment or the side effects you are experiencing, please speak to your prescribing clinician.
References
Su, Q.J., Ashenhurst, J.R., Xu, W. et al. Genetic predictors of GLP1 receptor agonist weight loss and side effects. Nature 653, 770–775 (2026). https://doi.org/10.1038/s41586-026-10330-z
23andMe Research Institute. Unlocking the Genetics of GLP-1 Medications: Why Your DNA Matters. 23andMe Blog, 8 April 2026. blog.23andme.com/articles/glp-1-medications-why-your-dna-matters
