The Same "Weight Loss Injection" but Different Results: The Boundary Between Those for Whom It Works and Those for Whom It Doesn't, as Revealed by DNA

It was hard to imagine a few years ago that "weight loss injections" would change the social atmosphere to this extent.
Mounjaro, Wegovy, Ozempic. These names are now mentioned not only in medical contexts but also in everyday conversations and on social media. Stories of people who have significantly lost weight have spread, dramatically altering the landscape of obesity treatment. However, behind the enthusiasm, there has always been a lingering sense of discomfort. Some people who started the same way experience remarkable weight loss, while others see little change. Some experience mild side effects, while others find it difficult to continue due to nausea and vomiting. Where does this difference come from?

A new study by the 23andMe research institute has provided a compelling answer to this question. The published paper suggests that genetic differences may play a role in the varying effectiveness of GLP-1-based drugs. The key point is not simply whether the drugs work or not. More accurately, the study suggests that genetic tendencies may partially reflect "how effective the drugs are" and "how likely certain side effects are to occur."

The focus was on two genes: GLP1R and GIPR.
GLP1R is involved with the GLP-1 receptor, essentially the "target" that the drug acts upon. People with certain mutations in this gene were found to show a tendency for greater average weight loss. However, it's important not to view this difference as magical. The study only indicates an average increase, and genes do not determine all aspects of weight loss. In fact, the research team itself acknowledges that the genetic contribution is present but limited.

Another important aspect is the side effects.
In discussions about GLP-1 drugs, there are as many voices saying "it's hard to lose weight" as there are saying "nausea is tough," "my stomach feels heavy," and "I can't eat." The study suggests that mutations in GIPR, in addition to GLP1R, may be related to nausea and vomiting. Notably, the GIPR mutation was prominent in tirzepatide-based drugs and was not observed in the same way with semaglutide-based drugs. This means that even drugs grouped under the "GLP-1 category" may have different genetic patterns affecting side effects due to differences in molecular design.

What emerges here is that obesity treatment is finally moving beyond the stage of "prescribing the same medication to everyone and seeing what happens."
Until now, obesity treatment has been a series of trial and error from the patient's perspective. If it works, continue. If it doesn't, change. If side effects are strong, stop. Reducing the "you won't know until you try" aspect even slightly would be a significant advancement in medicine. By combining genetic information with age, gender, medical history, dosage, and treatment duration, it's possible to make more precise predictions from the start, such as "this person is likely to respond well" or "this person may experience strong side effects."

However, it's too early to interpret this study as "a genetic test will immediately reveal the right medication for you."
This is also the point most prone to misinterpretation in social media and reporting. The results are indeed intriguing. However, external experts unanimously caution that the findings are not yet decisive enough to be directly applied in clinical settings. In fact, when explaining the differences in weight loss, non-genetic factors such as gender, type of medication, dosage, and treatment duration have a significant impact. In the research model, most of the explained variation was attributed to these non-genetic factors. While genes are an important clue, they do not monopolize the spotlight.

Moreover, it's important to calmly assess the study's limitations.
Much of the data is based on self-reporting, with a high proportion of female and European ancestry participants. While this makes the study large-scale and valuable, it does not mean it can be generalized to all races, regions, and clinical environments. Therefore, it's appropriate to understand this study as an "entry point to personalized obesity medicine" rather than an "answer."

Interestingly, the reactions on social media reflect this duality.
First, there's noticeable empathy from those who were on the "non-responsive side." In overseas patient communities, voices saying "I'm a non-responder," "I don't lose weight even with a calorie deficit," and "switching from Ozempic to Mounjaro didn't yield results" have been prominent. These posts provide new language, suggesting "it might be a difference in body type," to the struggles that were previously dismissed as personal effort deficiencies or lifestyle issues.

Next, there were reactions from those who have suffered from side effects, feeling that "an explanation has been found."
For those who couldn't continue due to severe nausea and vomiting, this study is not just academic news. It feels like they have gained some insight into why they alone suffered so much. Side effects are often treated as a matter of endurance. However, if genetic background is partially involved, it might not be a matter of endurance but rather a predisposed body. This shift in perspective is significant.

Meanwhile, doctors and researchers on social media are playing the role of tempering the enthusiasm.
The cautious view is that "precision medicine is approaching, but we haven't reached it yet."
The consensus is that "genetic factors can be an additional material, but the core of prediction remains age, gender, BMI, medication, and dosage."
At the same time, there are voices evaluating it as "a clear example of how target-level genetics can explain real-world response differences," with expectations and caution running simultaneously. While social media can be a hotbed of exaggeration, this time it holds significance in simultaneously visualizing patient experiences and expert sobriety.

What this study might truly change is not the drugs themselves but the "approach" of the medical side.
Previously, whether a treatment would work was partly left to chance. However, going forward, there is a possibility of moving towards an era where, in addition to genetic information, past medical history, metabolic state, treatment history, and lifestyle background are all considered to design "which drug, at what dosage, and with what explanation to start for this person." Obesity treatment is often consumed as a topic of beauty or trend, but its essence is the management of a chronic disease, and as personalization progresses, it gets closer to true medical care.

Ultimately, what this study conveys is not a simple story that genes determine everything.
Quite the opposite. It's not surprising that the effectiveness varies from person to person, and there are biologically explainable parts to that difference. And this difference cannot be measured solely by personal determination or willpower.
Breaking down the crude view that "only those who respond are correct" and "those who don't respond lack effort."
That is perhaps the most significant social implication of this study.

Discussions around GLP-1 drugs will likely continue to heat up.
New drugs will increase, applications will expand, and the market will grow further. In that context, what's important is not "selling the same hope to everyone" but "accurately conveying what reality is likely to occur for whom." This study has begun to draw the first map for that purpose. It's still rough, but it is indeed moving forward.
And the gap between success stories and failures on social media is finally starting to be treated as a difference that medicine should unravel, rather than just luck.

Fact Notes

The recent Nature paper analyzed the differences in weight loss effects and side effects of GLP-1 drugs based on self-reported data from 27,885 participants in the 23andMe study, with a median treatment duration of 8.3 months and a median weight loss of 11.7% of pre-treatment weight. The main genetic analysis was conducted on a narrowed group of 15,237 individuals from the European ancestry cohort with the necessary data.

The study found that GLP1R mutations were associated with "a slight but significant additional weight loss," and according to Reuters, the effect size was an average increase of 1.7 pounds for one copy and 3.3 pounds for two copies. Mutations in GLP1R and GIPR were also linked to nausea and vomiting, with GIPR's impact primarily observed in the tirzepatide group. In some individuals with both risk mutations, the odds of tirzepatide-related vomiting were estimated to be about 14.8 times higher.

However, the influence of non-genetic factors is significant, and the Nature paper reported that models including gender, type of medication, dosage, and treatment duration explained about 21.4% of the variance in weight loss, with another integrated model attributing most of the explained variance to non-genetic factors. External experts also evaluate that it is premature to use genetic information alone for treatment selection in clinical practice.

On social media, in the Reddit Mounjaro community, there was empathy from individuals identifying as non-responders, saying "I haven't lost much even after using it for over a year," while there was also an understanding that "there might be a DNA reason for those who experience severe nausea and vomiting." On X, cautious opinions such as "precision medicine is approaching, but we're not there yet" and "the additional value of genetic factors is not significant" were shared, alongside positive evaluations like "a good example of how target-level genetics can explain drug response differences."

Source URLs

The InfoMoney article was referenced as the starting point for how this study was reported.
https://www.infomoney.com.br/saude/genetica-pode-influenciar-a-eficacia-de-canetas-emagrecedoras-diz-pesquisa/

Original peer-reviewed paper. Used to confirm research design, number of subjects, main genetic mutations, median weight loss, contribution of non-genetic factors, and verification of replication analysis.
https://www.nature.com/articles/s41586-026-10330-z

Nature news article. Referenced to supplement the study's social significance and its positioning in personalized medicine.
https://www.nature.com/articles/d41586-026-01107-5

23andMe research institute's announcement. Used to confirm the research team's explanation, GLP-1 related report provision, and explanation of weight loss and nausea prediction ranges.
https://mediacenter.23andme.com/press-releases/new-23andme-research-institute-study-identifies-genetic-predictors-for-glp-1-weight-loss-efficacy-and-side-effects/

Reuters article. Used to organize the average effect size of GLP1R mutations and the vomiting risk with GIPR mutations in tirzepatide.
https://www.reuters.com/business/healthcare-pharmaceuticals/genetic-variations-linked-weight-loss-side-effects-glp-1-drugs-2026-04-10/

The Guardian article. Used to confirm cautious evaluations by external experts stating "the effect is clinically small" and "it's not yet the stage to use genetic information alone in everyday clinical practice."
https://www.theguardian.com/science/2026/apr/08/dna-could-help-explain-why-weight-loss-jabs-may-not-work

Washington Post article. Used to confirm the significance as precision medicine, additional weight loss range, comments from external experts, and the context of replication evaluation in All of Us.
https://www.washingtonpost.com/health/2026/04/08/glp1-gene-weight-loss-response-side-effects/

Scientific American article. Used to explain the mechanism of GLP1R/GIPR mutations and organize the background of GIPR involvement in tirzepatide.
https://www.scientificamerican.com/article/how-well-glp-1-weight-loss-drugs-work-may-depend-on-your-genetics/

Reddit Mounjaro thread. Used to confirm reactions from non-responder participants and perceptions of side effects.
https://www.reddit.com/r/Mounjaro/comments/1sg17pb/washington_post_if_you_arent_losing_weight_with/

Reactions on X. Used to confirm how both cautious and optimistic views are spreading.
https://x.com/DrMarthaGulati
https://x.com/aditharun_
https://x.com/YLeyfman