What your genes can (and can't) tell you about weight loss

In April 2026, researchers at the 23andMe Research Institute published a large genetic study in Nature examining why people respond so differently to GLP-1 medications such as semaglutide (Ozempic, Wegovy) and tirzepatide (Mounjaro, Zepbound).

Here is a straightforward look at what the study found, what it means, and what it does not (yet) mean for anyone starting or continuing GLP-1 treatment.

The reality: two genes do seem to matter

The researchers studied nearly 28,000 people who had used a GLP-1 medication and looked for genetic variants linked to how much weight they lost and how much nausea or vomiting they experienced.¹ Two findings stood out.

A variant in GLP1R, the gene that codes for the very receptor these drugs act on, was linked to slightly greater weight loss. People carrying a particular version of this gene lost, on average, an extra 0.76 kg per copy of the variant they carried. The same genetic region was also linked to a higher chance of nausea, which fits a pattern the researchers noted more broadly: people who experience more nausea on these medications also tend to lose somewhat more weight.¹

A variant in GIPR was linked to vomiting, but only in people taking tirzepatide, not semaglutide. This makes biological sense. Semaglutide acts on one hormone receptor (GLP-1), while tirzepatide acts on two (GLP-1 and GIP). The GIPR variant affects how well the GIP part of the drug can settle the stomach, which is why its effect only shows up in tirzepatide users.¹

Both of these are findings from a peer-reviewed, published study, and the GLP1R result was independently confirmed in a separate research cohort (All of Us) using medical record data rather than self-reported figures.¹ That is a meaningfully more robust form of evidence than a single self-report survey alone.

The reality: genetics is one piece of a much bigger picture

Here is the part that tends to get lost in the more excitable coverage. In this same study, genetics was a modest contributor compared with everything else that predicts how someone responds to treatment.

The researchers built a combined model using clinical, demographic and genetic information together. It explained around a quarter of the variation in weight loss outcomes, and the genetic variants contributed only a small slice of that.¹ Far larger predictors of outcome included:

1. Which drug was used (tirzepatide showed greater median weight loss than semaglutide in this cohort)
2. Sex (women showed somewhat greater average weight loss than men)
3. Existing health conditions such as type 2 diabetes, hypertension and fatty liver disease, each linked to somewhat lower efficacy
4. Dose and length of time on treatment

In other words, the study's headline is genuinely "we found genes that matter," not "we found the genes that explain why you're not losing weight." Those are different claims, and the difference matters if you are the one taking the medication.

What this doesn't mean: there is no genetic test that tells you which GLP-1 dose is right for you

This is the most important point for anyone reading the headlines and wondering whether they should get their DNA tested before starting treatment.

The study's authors themselves describe this as an early step towards precision medicine, not a finished tool.¹ A commercial interactive report based on these findings has been made available in the US, but only through a physician-supervised service, and it is explicitly designed to be reviewed together with a clinician rather than interpreted alone.² There is currently no equivalent test integrated into UK prescribing pathways, NHS or private, for GLP-1 medications. Your prescriber cannot currently order a genetic test to decide your starting dose, your likely weight loss, or your risk of side effects, because no such clinically validated pathway exists here yet.

What actually determines your dose and monitoring today is the same as it always has been: your health history, your current health conditions, how you respond as treatment progresses, and clinical guidance from your prescriber. That is not a lesser approach because it lacks a genetic test attached to it. It is simply the current evidence-based standard of care.

What this doesn't mean: side effects or slower progress are not "your fault," genetic or otherwise

If there is one thing worth taking from this research and applying practically, it is this. The study adds solid evidence that biological variation, not effort or willpower, explains a real part of why people respond differently to the same medication at the same dose.¹ Some of that variation appears to be genetic. Much more of it is explained by sex, existing health conditions, and straightforward clinical factors like dose and time on treatment.

If your experience does not match someone else's, or does not match what you expected, that is not a personal failing, and it is not something a DNA test would meaningfully explain away either. It is a reason to talk to your prescriber about how your individual treatment is progressing, not a reason to search for a genetic explanation on your own.

The takeaway

Genetics is a real and interesting piece of the GLP-1 story, and it is likely we will hear more about it as research continues. But right now, it is one contributing factor among several, it does not translate into a test you can act on in UK clinical practice, and it does not change what actually determines a safe, effective treatment plan: proper clinical assessment, appropriate dosing, and ongoing conversation with your prescriber.

If you have questions about how your own treatment is going, or about side effects you are experiencing, talk to your prescribing clinician.

References

1. 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
2. 23andMe Research Institute. Unlocking the Genetics of GLP-1 Medications: Why Your DNA Matters. 23andMe Blog, 8 April 2026. Unlocking the Genetics of GLP-1 Medications: Why Your DNA Matters