A landmark study published yesterday in Nature — the world's most prestigious scientific journal — may explain why your GLP-1 medication works brilliantly for your coworker but barely moves the scale for you. Researchers at the 23andMe Research Institute analyzed genetic data from 27,885 people who have used GLP-1 medications and identified specific gene variants that predict both how much weight you will lose and how severe your side effects will be.
The findings are striking. Among study participants, weight loss ranged from 6 percent to 20 percent of starting body weight depending on genetics and other factors. The chances of experiencing nausea or vomiting ranged from 5 percent to 78 percent. That is not a small difference — it is the difference between a life-changing treatment and an intolerable one. And for the first time, we have genetic data that helps explain why.
What the Study Found
The research team conducted a genome-wide association study (GWAS) — essentially scanning the entire genetic code of nearly 28,000 GLP-1 users to find patterns. They found two key results.
First, a variant in the GLP1R gene predicts greater weight loss. This is the gene that codes for the GLP-1 receptor — the exact protein that medications like Ozempic, Wegovy, and Foundayo bind to. People carrying one copy of a specific missense variant in this gene lost an average of 1.7 additional pounds compared to those without it. People with two copies lost over 3 additional pounds. That may sound modest, but it compounds over the months-long treatment period and represents a meaningful difference in outcomes.
Second, variants in both the GLP1R and GIPR genes predict nausea and vomiting risk. This is where it gets particularly interesting for patients choosing between medications. The GIPR gene association was specific to tirzepatide users — meaning patients on Mounjaro or Zepbound. The GLP1R variant affected nausea risk across all GLP-1 medications including semaglutide (Ozempic, Wegovy) and orforglipron (Foundayo).
In practical terms: if you carry certain GIPR variants and are considering a dual GIP/GLP-1 agonist like Zepbound, you may have a significantly higher nausea risk than someone on a GLP-1-only medication like Wegovy or Foundayo. This could meaningfully change which drug your prescriber recommends.
Why This Matters for Choosing Your Medication
Until now, choosing a GLP-1 medication has been largely trial and error. Your doctor picks a drug based on insurance coverage, general efficacy data, and your preferences (pill vs injection). If it does not work well or the side effects are unbearable, you switch. This study suggests a future where genetics inform that decision upfront.
Here is how the findings map to current medication choices:
If you are a strong GLP-1 responder (favorable GLP1R variant): Any GLP-1 medication should work well for you. The choice comes down to convenience and cost — Foundayo at $149 per month (daily pill, no fasting) versus injectable Wegovy at $249 per month (weekly shot, higher average weight loss).
If you are a weak GLP-1 responder: A dual-mechanism drug like Zepbound (tirzepatide) may be more effective because it activates both GLP-1 and GIP receptors, giving you two pathways to weight loss instead of one.
If you carry GIPR nausea variants: You may want to avoid tirzepatide (Mounjaro, Zepbound) and stick with semaglutide-based medications (Wegovy, Ozempic) or orforglipron (Foundayo), which do not activate the GIP receptor.
If you are nausea-sensitive regardless of genetics: Foundayo has a significant practical advantage. Because it is taken daily with food, dose adjustments happen faster and taking it with a meal reduces nausea for most patients. Compare that to a weekly injection where you cannot undo a dose once it is administered.
For a complete comparison of all these medications, see our [drug comparison page](/compare).
Can You Get Tested?
23andMe announced that it is releasing a new report called GLP-1 Medications Weight Loss and Nausea for members of its Total Health service. This report provides personalized insight into your expected weight loss and nausea risk based on these genetic findings.
If you are already a 23andMe customer with Total Health access, the report should be available now. If not, a 23andMe Health + Ancestry kit costs approximately $229 and would include access to these GLP-1 insights along with hundreds of other health reports.
It is worth noting that genetic testing is not required to use GLP-1 medications. The study identifies statistical tendencies across populations — it does not guarantee individual outcomes. Plenty of people without the favorable GLP1R variant still lose significant weight, and plenty of people with GIPR nausea variants tolerate tirzepatide just fine. But if you are deciding between medications and want every piece of information available, this data is now part of the picture.
What This Does Not Change
A few important caveats. This study does not mean you should stop your current GLP-1 medication based on genetics alone. If your treatment is working, stay on it. Genetic risk is probabilistic, not deterministic.
The study also does not change the fact that lifestyle factors — diet, exercise, sleep, stress — remain powerful predictors of GLP-1 success regardless of genetics. Our [exercise and GLP-1 guide](/guides/glp1-and-exercise) covers how to maximize results through movement, and our [food noise guide](/guides/food-noise) addresses the appetite changes most patients experience.
Finally, the study reinforces something we have been saying for months: there is no single best GLP-1 medication for everyone. The right drug depends on your body, your budget, your insurance, and now, potentially, your genetics. That is exactly why independent comparison tools like ours exist — to help you evaluate all the options based on your specific situation.
The Bottom Line
For the first time, we have large-scale genetic evidence explaining why GLP-1 weight loss varies so dramatically between individuals. If you are considering starting GLP-1 therapy, this study adds one more data point to your decision. If you are already on a GLP-1 and not seeing results after 3-6 months, genetics may be part of the explanation — and switching to a different mechanism (GLP-1 only versus dual GIP/GLP-1) could help.
We will continue covering the clinical research as it develops. For now, the best action you can take is to choose a provider that offers comprehensive medical support, monitors your progress, and is willing to adjust your treatment plan based on your individual response. Our [best GLP-1 providers ranking](/best) evaluates all 32 programs on exactly these criteria.
The era of one-size-fits-all weight loss medication is ending. What comes next is more personalized, more effective, and more informed by science than anything before it.