Why GLP‑1s vary

Glucagon-like peptide-1 drugs copy a gut hormone that slows stomach emptying, boosts fullness and helps control blood sugar, but they do not produce the same result in every patient. Clinical trials summarized in reporting this week put the share of people who do not get substantial weight loss at about 10% to 15%. (ksl.com) (pmc.ncbi.nlm.nih.gov) A Nature study published April 8, 2026, looked for one reason why by analyzing self-reported weight loss and side effects in 27,885 people who had used semaglutide or tirzepatide. The researchers found a variant in the GLP1R gene tied to greater weight loss, with about 0.76 kilograms of extra loss per copy of the effect allele. (nature.com) (mediacenter.23andme.com) The same study linked nausea or vomiting to variation in two genes, GLP1R and GIPR, and the GIPR signal showed up only in people taking tirzepatide, sold as Zepbound and Mounjaro. Science News reported April 16 that the gene effects were modest, not a simple yes-or-no answer for who will respond. (nature.com) (sciencenews.org) Doctors have known from trials that average results can be large while individual results vary widely. Reporting from CNN, republished by KSL on April 15, said people labeled nonresponders in trials generally lost less than 5% of body weight even as many others on the same drugs lost far more. (ksl.com) (mediacenter.23andme.com) Genes are only part of the picture. The Nature paper says age, sex, starting weight, the specific drug, dose escalation, other medical conditions and whether a patient can stay on treatment also shape how much weight comes off and whether stomach side effects force a stop. (nature.com) (pmc.ncbi.nlm.nih.gov) The newer genetics work lands as researchers keep finding benefits beyond the scale. A 2025 review in Cell Reports Medicine said glucagon-like peptide-1 medicines improve outcomes in cardiovascular disease, chronic kidney disease, liver disease, sleep apnea and osteoarthritis, with some benefits partly independent of weight loss. (pmc.ncbi.nlm.nih.gov) That broader case already shows up in regulators and major trials. The Food and Drug Administration said in August 2025 that Wegovy, the semaglutide brand for obesity, won approval to treat metabolic dysfunction-associated steatohepatitis with moderate-to-advanced fibrosis, and the SELECT trial previously found semaglutide lowered the risk of cardiovascular death, heart attack or stroke in adults with overweight or obesity and prior cardiovascular disease who did not have diabetes. (fda.gov) (nejm.org) Researchers are not yet saying patients should get routine genetic screening before starting these drugs. The April 2026 findings point instead to a more tailored approach, where prescribing may eventually weigh likely weight loss, side-effect risk and benefits to the heart or liver together, not just the number on a scale. (nature.com) (sciencenews.org)