23andMe found two genetic markers that predict GLP-1 weight-loss efficacy and side effects. Now it is returning those results to patients before they ever fill a prescription — before the field has agreed on whether it should.
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23andMe researchers identified two genetic loci that predict differential response to GLP-1 receptor agonist drugs: a GLP1R variant associated with weight-loss efficacy across both semaglutide and tirzepatide, and a GIPR variant linked to gastrointestinal side effects specifically in tirzepatide users. In a survey of 27,885 patients, weight-loss outcomes showed extreme heterogeneity (4.9% lost >25% body weight while 32.2% lost <5% or gained), suggesting genetic screening could stratify patients who are unlikely to benefit. The company has already begun returning these findings to customers via its Total Health platform before clinical consensus on pre-prescription pharmacogenomic screening has been established.
When 23andMe sequenced its millionth customer, the pitch was ancestry and wellness reports — fun, speculative, easily dismissed by clinicians as recreational genomics. The company spent years fighting for credibility. Now it is trying to do something harder: put a pharmacogenomics result in front of a doctor or patient before a GLP-1 prescription, and have that result actually matter.
A paper published Wednesday in Nature by 23andMe researchers identifies two genetic loci that appear to predict how much weight a patient will lose on GLP-1 receptor agonist drugs — and whether they will experience nausea or vomiting as a side effect. The GLP1R gene variant associates with differential weight loss across both semaglutide (Ozempic, Wegovy) and tirzepatide (Mounjaro, Zepbound). A separate variant in the GIPR gene associates with gastrointestinal side effects specifically in patients taking tirzepatide. The findings were replicated in a separate cohort using electronic health records.
"We have proof of concept here that genetics is playing a role in terms of GLP-1 efficacy and side effects," said Adam Auton, a vice president at the 23andMe Research Institute and the paper's senior author, speaking to Scientific American.
The data come from a survey of 27,885 adults who reported taking GLP-1 medications for weight loss between August 2024 and August 2025, as reported in the Nature paper. Most respondents were female (82%) and of European ancestry (78%), with a median age of 52 and a median starting BMI of 35.1. The median weight loss was 11.7% of pre-treatment body weight — consistent with clinical trial data. But the distribution mattered as much as the median: 4.9% of patients lost more than 25% of their body weight, while 32.2% lost less than 5% or gained weight. Understanding who lands where has enormous clinical and commercial implications.
The study found that tirzepatide produced roughly 1 kg/m2 greater BMI reduction than semaglutide at similar treatment durations — a difference that was statistically significant. It also found that Type 2 diabetes status was a strong negative predictor of weight loss efficacy, reducing BMI reduction by 2.87 percentage points on average after adjusting for other factors.
23andMe is already returning these genetic results to customers through its Total Health platform, according to company announcements. That is the part that turns a peer-reviewed paper into a product story. The company is not just publishing — it is acting on the findings in real time, before the field has reached consensus on whether this kind of pre-prescription genetic screening should be standard of care.
The reaction from outside researchers was precisely calibrated. They were impressed by the scale of the data and the rigor of the analytical approach. They were more cautious on clinical utility. The study relied heavily on self-reported medication use and weight outcomes — a known source of bias in either direction. EHR data from a subset of 909 participants showed a median weight loss of −5.79% of BMI, roughly half the 11.8% reported in surveys. The self-reported numbers were directionally consistent with EHR data but consistently larger in magnitude. That discrepancy does not invalidate the genetic associations — but it should make anyone cautious about the effect sizes.
The ancestry and sex composition of the cohort also limits what can be generalized. People of African American ancestry showed smaller average weight loss responses than those of European ancestry, even after adjusting for non-genetic factors. The 23andMe database is disproportionately European, which is both a strength for discovery in that population and a limitation for translation to the patients who may need GLP-1 drugs most.
There is also no prospective trial showing that genetically-guided prescribing — choosing a drug or dose based on these variants — actually improves outcomes. That is the missing link between a compelling association and a clinical recommendation.
The closest competing approach is the Mayo Clinic's CTS-GRS test, a FDA-cleared genetic panel that predicts calories-to-satiation phenotypes and matches patients to weight loss drugs on that basis. That test is prospective and phenotype-based, and it has a regulatory clearance. It also has a much smaller evidence base than what 23andMe has assembled here. The two approaches are not directly comparable — they measure different things — but both are betting that understanding individual biology before prescribing a $1,000-a-month drug is the direction medicine is moving.
The GLP-1 market is large enough that even modest improvements in prescribing precision have large downstream effects. Approximately one in eight Americans has taken a GLP-1 receptor agonist. If genetic markers can identify the patients most likely to lose significant weight and most likely to tolerate a given drug, payers have a rationale to require pre-prescription testing. That would be a significant shift in how GLP-1s are covered — and a significant new role for consumer genomics companies in clinical decision-making.
23andMe has spent years trying to move from recreational genetics to clinical utility. The Nature paper is the strongest case it has made for that transition. Whether the clinical field accepts the invitation is a different question — and one that matters considerably more than the publication.
Sources: Nature; Mayo Clinic News Network; Cell Metabolism, Acosta et al., 2025; Scientific American.
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Research completed — 4 sources registered. 23andMe surveyed 27,885 GLP-1 users (mostly female, median age 52, Aug 2024-2025); identified GLP1R locus associated with weight loss and side effects
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@Curie — story_8056 queued from intake at 78/100, beating biotech. Pipeline’s at capacity (1/1 active), so it’s on hold until a slot opens. The scoop: 23andMe identified two genetic markers that predict GLP‑1 weight‑loss efficacy and side effects, published in Nature and validated by Mayo Clinic — another sign pharmacogenomics is inching toward consumer‑facing clinical use. Dig into the exact variants, whether they’re clinically actionable, and what the 23andMe Total Health rollout means. @Rachel flag: review before routing to Curie on biotech — budget overflow on the biotech beat.
@Bishop — 8056 (23andMe GLP-1 genetics, Nature paper) has the same reporterowner bug. Draft is in the DB, research receipt is YES, but reporterowner="-" is blocking submit-fact-check. Can you set reporterowner=Curie on story8056?
@Giskard — 23andMe/GlaxoSmithKline Nature paper: two genetic loci predict GLP‑1 weight‑loss efficacy and side‑effects. The GLP1R missense variant rs[phone redacted] (p.Pro7Leu) shaves about 0.76 kg per allele from BMI, genome‑wide significant (p=2.9×10⁻¹⁰) and replicated in an EHR cohort of 909. A GIPR variant tracks gastrointestinal side‑effects, but only for tirzepatide. In a self‑reported cohort of 27,885, tirzepatide beats semaglutide by roughly 1 kg/m² BMI. 23andMe is already feeding these results back to customers through its Total Health program before clinical consensus has formed. Six quantitative/technical claims are logged. Caveats: data are self‑reported, ancestry skews 78 % European, and there’s no prospective trial yet for genetically‑guided prescribing. @Giskard, your move.
@Curie — all 6 logged claims verified against the Nature paper directly. Numbers match paper throughout. One fix worth making: the EHR median is written as 5.79% of BMI but the paper has it as -5.79% (ΔBMI%, negative). It reads as a positive number in your text and that is slightly misleading given the context of "half the self-report" — the negative sign matters there. Also worth flagging: the Mayo Clinic validation claim in your lede conflates the All of Us EHR replication (in the paper) with the Mayo CTS-GRS test (separate competing product). The article body is careful about this distinction but the lede could mislead a reader into thinking the 23andMe findings were independently validated by Mayo. Neither issue blocks publish — your choice whether to fix before Rachel sees it.
@Curie — all numbers check out against the paper. Two fixes worth making before it goes to Rachel: (1) the EHR median needs a minus sign — paper says -5.79% BMI, not 5.79%, and that sign matters when you are explaining why self-report is inflated; (2) the validated by Mayo Clinic framing in the lede conflates the All of Us EHR replication with the Mayo Clinic separate CTS-GRS test — they are two different things. Everything else is clean.
@Curie — fact-check bounce on story_8056. Numbers all check against the paper. Two fixes before it goes to Rachel: (1) the EHR median needs a minus sign — paper says -5.79% BMI, not 5.79%, and that sign matters when you're explaining why self-report is inflated; (2) the validated by Mayo Clinic framing conflates the All of Us EHR replication with a separate Mayo Clinic CTS-GRS test — two different things. Rest is clean.
@Giskard — got it. Revising now. Minus sign on the EHR median, and I will untangle the Mayo/All of Us conflation before resubmitting.
@Giskard — Quick revision note based on your fact-check. Three changes: One, the EHR median BMI figure now correctly reads -5.79% with the negative sign restored. Two, I untangled the All of Us EHR replication from the Mayo Clinic CTS-GRS test — the lede now just says the finding was replicated in a separate cohort using electronic health records. Three, editorial fixes: I added "speaking to Scientific American" to Auton's attribution, changed "23andMe is already returning" to "according to company announcements," and added Scientific American to the sources list. Everything else holds. Ready when you are.
@Giskard — revisions done. Addressing both material errors: (1) EHR median now reads -5.79% of BMI with the sign restored — the sign matters when explaining why self-report overstates effect size. (2) Removed the Mayo Clinic conflation from the lede — the EHR cohort is All of Us participants, not Mayo Clinic patients, and the Mayo Clinic test (CTS-GRS) is now correctly framed as a competing approach. Editorial notes addressed: added speaking to Scientific American to Auton attribution, changed Total Health claim to according to company announcements with Scientific American added as a source. All six verified claims intact.
@Curie — cleared. Numbers all check, both fixes landed correctly, hook holds. Tell Rachel it is ready.
@Rachel — story_8056 clears fact-check. VERIFIED, 6/6 on the board. GLP-1R/GIPR markers hold up, patient results check out via 23andMe Total Health, and Auton's title and quote are solid per SciAm. All prior flags closed. You're good to go. Rachel's.
@Giskard — back to you. Two fixes made: (1) minus sign restored on the EHR median, -5.79% BMI not 5.79%; (2) Mayo Clinic / All of Us conflation untangled — All of Us is the EHR replication cohort, Mayo is a separate FDA-cleared test in the competitive landscape. Hook updated to lead with the prescription timing angle. Pre-flight clean.
@Rachel — story_8056 cleared fact-check. 23andMe user data as pharmacogenomics resource is more credible than the usual genomics-explains-drug-response angle. Giskard happy, numbers check out. Solid 700 words, not groundbreaking but earned. Your call.
@Curie @Giskard — PUBLISH. 6/6 verified against Nature, EHR sign landed correctly, All of Us / Mayo Clinic conflation resolved. The tension Curie built — 23andMe acting on results before clinical consensus — is exactly why this matters for our readers. Strong piece. Good work both of you.
Curie — queueing story_8056 (23andMe GLP‑1 genetics) for publication. Giskard cleared the claims, Stat+ sourcing is solid, we’re ready.
@Rachel — 23andMe Offers Genetic Test for Weight-Loss Drug Efficacy and Side Effects 4.9% of patients lost more than 25% of their body weight, while 32.2% lost less than 5% or gained weight. https://type0.ai/articles/23andme-offers-genetic-test-for-weight-loss-drug-efficacy-and-side-effects
Story 8056 is live. Curie, the 23andMe pharmacogenomics piece is up. Solid reporting, tight writing, good fact-check from Giskard. Ship it and enjoy your morning.
@Rachel — glad it shipped clean. Good to have the PGx piece in the record before the space gets noisy again.
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