GLP1ROzempic and your genes: can DNA predict how much you will lose?
Two friends start the same weekly shot in the same month. Six months later, one has lost 20 kilos. The other has lost 4 and feels sick half the time.
If you are about to start Ozempic, Wegovy or Mounjaro, you want to know which friend you will be. And you may have seen DNA tests that promise to tell you. Here is what the science says.
The problem: same shot, very different results
In a big trial, about 2,000 adults took semaglutide (Wegovy) or a placebo, a fake shot, for 68 weeks. On average, people on the drug lost 15 percent of their weight, and people on the placebo lost 2 percent. But look at how spread out the results were:
So the real question is not "does it work?" but "will it work for me?".
Why it happens: what decides your result
How the shots work
After you eat, your gut sends a hormone called GLP-1 to your brain. Its message: "that's enough food". Ozempic and Wegovy (semaglutide) and Mounjaro and Zepbound (tirzepatide) copy this hormone and make the message stronger, so you feel full sooner and think about food less.
To work, the drug has to attach to your cells, like a key in a lock. The lock is made by a gene called GLP1R. If DNA changes the result, this gene is the first place to look.
Genes: a small effect
In 2024, 23andMe asked almost 28,000 of its customers who used these shots how much weight they lost. On average it was about 11 percent in eight months. Then researchers searched their DNA.
They found one clear signal, in the "lock" gene GLP1R. People with one version of it lost about 0.8 kilos more per copy, so about 1.5 kilos with two copies. Real, but small next to a 16-kilo gap between two friends. A second study of about 11,000 people in six countries found no gene that predicted the result at all. Even people with a high genetic risk for obesity lost about as much as everyone else.
What matters more than genes
The same 23andMe study measured other things, and they mattered more:
| What | How it changes the result |
|---|---|
| The drug | Tirzepatide (Mounjaro, Zepbound) gave more loss than semaglutide |
| Sex | Women lost more than men: about 12% vs 10% |
| Diabetes | People with type 2 diabetes lose less: about 10% vs 15% in trials |
| Other conditions | Fatty liver or high blood pressure: less loss |
| Age | A little less loss with every 10 years of age |
| The GLP1R gene | About 0.8 kg more per copy |
Even all of this together explained only about a quarter of the difference between people. The rest is still a mystery.
Where genes matter more: nausea
Nausea is the most common side effect. Here genes play a bigger role. People with certain versions of the GLP1R gene were more likely to feel sick or throw up, and on tirzepatide a second gene added to the risk. One surprise: people who felt more nausea also tended to lose more weight. The same strong signal that kills appetite can upset the stomach.
What to do
Before and during the shots
No test today can predict your result. The best gene moves it by about a kilo. A Mayo Clinic test is in the works, but it has only been tried on small groups of 50 and 110 people.
Check the table: your sex, diabetes and the drug shape what is normal for you. Not the best before-and-after photos online.
They matter more than your genes.
It is partly in your genes, not a weakness, and your doctor can help.
In the trial, people regained two thirds of the lost weight within a year of stopping. We explain why, and what helps, in why lost weight comes back.
Sources
- Wilding JPH, Batterham RL, Calanna S, et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). New England Journal of Medicine, 2021. PubMed 33567185
- Su QJ, Ashenhurst JR, Xu W, et al. Genetic predictors of GLP1 receptor agonist weight loss and side effects. Nature, 2026. PubMed 41951734
- German J, Cordioli M, Tozzo V, et al. Association between plausible genetic factors and weight loss from GLP1-RA and bariatric surgery. Nature Medicine, 2025. PubMed 40251273
- Davies M, Færch L, Jeppesen OK, et al. Semaglutide 2.4 mg once a week in adults with overweight or obesity, and type 2 diabetes (STEP 2). Lancet, 2021. PubMed 33667417
- Cifuentes L, Anazco D, O'Connor T, et al. Genetic and physiological insights into satiation variability predict responses to obesity treatment. Cell Metabolism, 2025. PubMed 40482646
- Wilding JPH, Batterham RL, Davies M, et al. Weight regain and cardiometabolic effects after withdrawal of semaglutide: the STEP 1 trial extension. Diabetes, Obesity and Metabolism, 2022. PubMed 35441470
