New study reveals lifelong use of weight-loss drugs like Mounjaro and Wegovy may be necessary
A New Study Offers Clues About Why GLP-1 Weight Loss Varies
Wegovy and Mounjaro have changed the way doctors approach obesity treatment. Yet one question remains common: why do some people lose much more weight than others on these medications?
A major study published in Nature in May 2026 provides part of the answer.
Researchers analyzed genetic and treatment data from more than 15,000 people taking GLP-1-based medications. The study found that certain genetic differences were associated with greater weight loss and with the likelihood of experiencing side effects such as nausea and vomiting.
That does not mean your genes determine whether Wegovy or Mounjaro will work.
Instead, the research suggests that individual biology may be one of several factors that influence treatment response.
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How Wegovy and Mounjaro Help With Weight Loss
Wegovy contains semaglutide, a GLP-1 receptor agonist.
Mounjaro contains tirzepatide, which acts on both the GLP-1 and GIP receptors.
These medicines affect appetite and other metabolic processes. They can help people feel fuller and reduce food intake.
But the amount of weight lost differs substantially between individuals.
That variation is one reason researchers are increasingly interested in personalized obesity treatment.
What the 2026 Genetics Study Found
The Nature study analyzed data from 15,237 people who had taken GLP-1 medications and had genetic information available.
Participants reported a median weight loss equivalent to about 11.7% of their starting body weight after a median treatment period of approximately 8.3 months.
The researchers identified a genetic variant in the GLP1R gene that was associated with greater BMI reduction.
Each copy of the relevant variant was associated with an additional estimated 0.76 kg of weight loss on average.
That is statistically meaningful, but it is not large enough to explain all of the differences seen between patients.
Genetics Are Only One Part of the Picture
The study does not suggest that a genetic test can currently tell someone exactly how much weight they will lose.
Many other factors can affect treatment response.
These include:
- The medication being used
- The dose and treatment duration
- Eating habits
- Physical activity
- Age
- Existing medical conditions
- Treatment adherence
- Individual biological differences
The study also found that women experienced greater median BMI reduction than men in the analyzed population. However, that does not mean every woman will respond better than every man.
This distinction matters because obesity treatment is highly individual.
Genetics May Also Influence Side Effects
The researchers found genetic associations involving nausea and vomiting.
For example, particular variants around the GLP1R and GIPR genes were associated with differences in side-effect risk. The study found that some genetic profiles were linked with a higher likelihood of nausea or vomiting.
This is an important finding because treatment effectiveness is only one part of the equation.
A medication that produces substantial weight loss but causes difficult side effects may not be suitable for every patient.
Does This Mean Genetic Testing Will Choose Your Weight-Loss Drug?
Not yet.
The research is an important step toward what scientists call precision medicine, where treatment could eventually be tailored more closely to an individual’s biology.
But the findings do not establish a routine genetic test that doctors can currently use to select Wegovy, Mounjaro or another obesity medication.
More research is needed before genetic information becomes a standard part of prescribing decisions.
Wegovy, Mounjaro and Individual Response
The study also found that people taking tirzepatide had greater median BMI reduction than those taking semaglutide in the analyzed real-world population. The researchers reported median BMI reductions of approximately 4.75 versus 3.71 kg/m² respectively.
However, these findings should not be interpreted as a simple winner-takes-all comparison.
Clinical results depend on the population studied, dose, duration, adherence and other factors.
The same medication can produce very different outcomes in different people.
What This Means for People Considering GLP-1 Treatment
The most useful message from this research is simple:
There is no single weight-loss response that applies to everyone.
Some people may lose substantial amounts of weight. Others may experience a more modest response.
Genetic differences may help explain part of that variation, but they are not the complete explanation.
If a person is considering a GLP-1 medication, treatment decisions should be made with a qualified healthcare professional based on medical history, weight-related health risks, medication suitability and expected benefits and risks.
Frequently Asked Questions
Why does Wegovy work better for some people than others?
Several factors can influence response, including medication, dose, treatment duration, adherence, lifestyle and individual biology. The 2026 Nature study suggests that genetics may also contribute.
Can genetics predict how much weight I will lose?
Not reliably at present. The research identifies genetic associations, but it does not provide a routine clinical test that can accurately predict an individual’s final weight loss.
Does Mounjaro work better than Wegovy?
The 2026 genetic study found greater median BMI reduction among tirzepatide users than semaglutide users in its analyzed population. That does not mean one medicine is automatically better for every individual.
Can GLP-1 drugs cause nausea?
Yes. Nausea and other gastrointestinal side effects are among the known effects of GLP-1-based medicines. The 2026 study also found genetic associations with nausea and vomiting.
Will precision medicine change obesity treatment?
It could. Researchers hope that genetic and other biological information may eventually help doctors personalize treatment. However, this approach remains an area of research.
Final Takeaway
Wegovy and Mounjaro can produce significant weight loss, but the response is not identical for everyone.
The new Nature research adds an important piece to that puzzle by showing that genetic differences may influence both weight-loss response and certain side effects.
For now, genetics should be viewed as one factor rather than a complete explanation.
The future of obesity treatment may become increasingly personalized, but clinical judgment, appropriate medication selection and long-term lifestyle support remain central to successful treatment.
Medical note: This article is for educational purposes only. Prescription weight-loss medicines should be used under the guidance of a qualified healthcare professional.
References
- Nature — “Genetic predictors of GLP1 receptor agonist weight loss and side effects.”
- Nature, May 21, 2026 — Study of genetic predictors of GLP-1 treatment response.
- FDA — Wegovy prescribing and regulatory information.
Written by Ravi Tiku
Publisher & Author | 38 Years of Pharmaceutical Sales Experience
[Medical information note: This article is for general educational purposes and is not a substitute for professional medical advice.]