Some patients don’t respond
In clinical trials about 10–15% of people on GLP‑1 drugs are considered ‘non‑responders’ because they don’t lose at least 5% of body weight, so the drugs are powerful but not universally effective (bostonglobe.com). That’s a useful benchmark if you’re tracking expectations—if you don’t hit 5% loss, clinical teams often reassess dosing, concurrent lifestyle support, or alternative strategies (bostonglobe.com).
These drugs copy gut hormones that tell your brain “meal’s over” and slow how fast food leaves your stomach, which is why many people feel full sooner on semaglutide or tirzepatide than they do on diet changes alone. In the Food and Drug Administration label, Wegovy is approved only as an add-on to a reduced-calorie diet and increased physical activity, not as a stand-alone shortcut. (accessdata.fda.gov) The benchmark doctors often watch is 5% of starting body weight, because that is the cutoff built into major obesity drug trials and older obesity-treatment guidelines. The Endocrine Society says if a patient has lost 5% or more after three months on a weight-loss drug, treatment can continue, and if not, clinicians should consider stopping or switching. (endocrine.org) That 5% line can sound small until you see how trials are designed. In the 1,961-person STEP 1 trial, semaglutide’s co-primary end points were percent weight change and whether patients lost at least 5% of body weight by week 68. (nejm.org) Most people on semaglutide in that trial cleared the line, but not everyone did. At week 68, 86.4% of participants on semaglutide lost at least 5% of body weight, which means about 13.6% did not hit that mark even with weekly injections plus lifestyle counseling. (nejm.org) Tirzepatide generally posts even bigger averages, but it also is not universal. In the 2,539-person SURMOUNT-1 trial, tirzepatide’s co-primary end points used the same 5% threshold, and mean weight loss at week 72 ranged from 15.0% at 5 milligrams to 20.9% at 15 milligrams. (nejm.org) The label for Zepbound says patients start at 2.5 milligrams once a week for four weeks, then move up in 2.5-milligram steps, with 5, 10, or 15 milligrams used for long-term weight reduction. The same label tells prescribers to consider both treatment response and tolerability when choosing the maintenance dose, which is why a slow or weak response often triggers a dose review before anyone declares the drug a failure. (pi.lilly.com) A “non-responder” label also does not mean the drug did nothing. The American Gastroenterological Association used a lower 3% threshold as the minimally important difference over lifestyle treatment alone, so a person can miss the 5% trial benchmark and still have a medically meaningful change. (aafp.org) Doctors also look for reasons the scale is lagging that have nothing to do with willpower. The Endocrine Society guideline says obesity treatment should combine medication with diet, exercise, and behavioral change, and it also warns clinicians to review other drugs that can push weight up, including some antidepressants, antipsychotics, and seizure medicines. (endocrine.org) The bigger picture is that these medicines are powerful on average, not magical for every individual body. A 2025 JAMA summary of randomized trials covering about 15,500 adults without diabetes found that all 12 glucagon-like peptide-1 receptor agonists studied lowered body mass, but the size of the effect varied by drug, with tirzepatide producing the largest losses among the three marketed agents it highlighted. (jamanetwork.com) So when someone says a glucagon-like peptide-1 drug “didn’t work,” the real question is usually more specific: how much weight was lost, at what dose, after how many weeks, with what side effects, and alongside what lifestyle support. In obesity medicine, those details decide whether the next move is patience, a higher maintenance dose, a different medication, or a different treatment plan entirely. (pi.lilly.com)
