# GLP-1 weight loss timeline from the studies *Guide · 2026-10-22 · https://undiet.app/guides/glp1-weight-loss-timeline* What the two largest trials of weekly semaglutide and tirzepatide actually reported: how many people, how long, the dose escalation, the average loss at the end, how many reached 5, 10, 15 or 20 percent, and what a week by week timeline can and cannot be read from them. ## Two trials, one honest timeline Most GLP-1 timelines on the web are a smooth curve with a number on every week. The trials that curve is drawn from did not publish a number for every week, so this guide stays with what they did report. The two biggest are STEP 1, for weekly semaglutide 2.4 mg, and SURMOUNT 1, for weekly tirzepatide. Both compared the medication with a placebo injection in adults with obesity, or overweight with a related condition. ## Who was in them, how long STEP 1 enrolled 1961 adults, assigned two to one to semaglutide 2.4 mg or placebo, for 68 weeks. The first 16 weeks were dose escalation, the step up from a small starting dose to the full one. SURMOUNT 1 enrolled 2539 adults, assigned equally to tirzepatide 5 mg, 10 mg, 15 mg or placebo, for 72 weeks. Its escalation period was 20 weeks, and the average starting weight was 104.8 kg. Everyone in both trials also got lifestyle counselling, a reduced calorie diet and an activity goal. The numbers below are the medication plus that, not the medication alone. ## The first months: the dose steps up In both trials the first stretch is escalation, 16 weeks in STEP 1 and 20 weeks in SURMOUNT 1. Your doctor sets the schedule for you; the trials only tell you how long theirs took. The published figures show the average weight falling through escalation and on past it, but the abstracts give no value for week 4, week 12 or week 20. Any week by week table you find elsewhere is read off a chart or invented. What you can keep from this is the shape of the question. The early weeks are where appetite and feeling change fastest, which is why Undiet logs both beside the weight. ## Week 68 and week 72: the endpoints STEP 1 reported a mean change of 14.9% with semaglutide against 2.4% with placebo at week 68, a difference of 12.4 percentage points. In kilograms that was 15.3 kg against 2.6 kg. SURMOUNT 1 reported 15.0% with tirzepatide 5 mg, 19.5% with 10 mg and 20.9% with 15 mg at week 72, against 3.1% with placebo. Those are averages of large groups. They are the best published anchor for a timeline, and they are not a forecast for one person; [where the numbers come from](https://undiet.app/guides/where-the-numbers-come-from) explains how the site draws every curve from a study like these. ## How many people got there In STEP 1, 86.4% of people on semaglutide lost at least 5% of their starting weight, 69.1% lost at least 10% and 50.5% lost at least 15%. On placebo those shares were 31.5%, 12.0% and 4.9%. In SURMOUNT 1, at least 5% was reached by 85%, 89% and 91% of people on the three tirzepatide doses, against 35% on placebo. At least 20% was reached by 50% on 10 mg and 57% on 15 mg, against 3% on placebo. Read the other side of each number too. Roughly one in seven people on semaglutide did not reach 5%, and about half did not reach 15%, which is a wide spread hiding under one average. ## Side effects, as the trials counted them The trials counted people who stopped because of gastrointestinal side effects. In STEP 1 that was 4.5% on semaglutide against 0.8% on placebo; in SURMOUNT 1 it was 4.3%, 7.1% and 6.2% on the three tirzepatide doses against 2.6% on placebo. Nausea, constipation and the rest were common and mostly mild to moderate in both trials. Undiet logs a queasy day as a feeling score with a note, not as a medical record, and what you do about it is a conversation with your doctor. ## What happened after the last dose STEP 1 is also the trial that kept watching after treatment stopped. A year off the medication, the group had regained two thirds of what it lost, on average. That stretch is the subject of its own guide, [After the last dose](https://undiet.app/guides/after-the-last-dose), and of the [GLP-1 page](https://undiet.app/glp1), because it is the part most apps leave blank. ## Keeping your own timeline The trial averages are the backdrop; your line is the point. In Undiet you mark the medication from the catalog, [GLP-1 therapy](https://undiet.app/diets/glp1-therapy) or the exact one such as [Wegovy](https://undiet.app/diets/wegovy-semaglutide), [Mounjaro](https://undiet.app/diets/mounjaro-tirzepatide) or [Zepbound](https://undiet.app/diets/zepbound-tirzepatide), and from that day it is a period on your timeline. Each dose is a diary entry with the strength and the date, and each day carries your weight, appetite and feeling. Weekly progress photos stay on the phone, and [the photo guide](https://undiet.app/guides/progress-photos-on-glp1) explains how to take them. If you are also deciding what to eat alongside the medication, [Find my diet](https://undiet.app/find-my-diet) asks about GLP-1 in its last question and puts the medication entry at the top of the shortlist. ## A note on advice Undiet describes programs and records what you log. It does not suggest a medication, a dose or a schedule, and nothing on a timeline is a reason to change one. Sources: Wilding et al., N Engl J Med 2021 (STEP 1); Jastreboff et al., N Engl J Med 2022 (SURMOUNT 1); Wilding et al., Diabetes Obes Metab 2022 (the STEP 1 extension). ## Programs in this guide - [GLP1 Therapy](https://undiet.app/undiet/diets/glp1-therapy.md): A general tracking entry for anyone using a GLP1 receptor agonist medication for weight management. - [Wegovy (semaglutide)](https://undiet.app/undiet/diets/wegovy-semaglutide.md): A once-weekly injectable GLP-1 medication used for weight management and type 2 diabetes. Info only. Decisions belong with your doctor. - [Ozempic (semaglutide)](https://undiet.app/undiet/diets/ozempic-semaglutide.md): A weekly semaglutide injection labelled in the US for type 2 diabetes, not for weight management. - [Mounjaro (tirzepatide)](https://undiet.app/undiet/diets/mounjaro-tirzepatide.md): A weekly tirzepatide injection labelled in the US for type 2 diabetes, while the EU label also covers weight. - [Zepbound (tirzepatide)](https://undiet.app/undiet/diets/zepbound-tirzepatide.md): A once-weekly injectable GLP-1/GIP medication for weight management and type 2 diabetes. Info only. Talk to your doctor. More guides: https://undiet.app/undiet/guides.md. Find my diet in five taps: https://undiet.app/find-my-diet. Free on iPhone (https://apps.apple.com/app/id1490849895) and Android (https://play.google.com/store/apps/details?id=be.krnic.undiet). Undiet describes programs and records what you log. It does not give medical advice. --- Any diet. No calorie counting. Your weight, your effort and every diet you try, on one timeline. Undiet is a tracking companion, not a medical service. For people aged 16 and over. Made by Krnic CommV, Gent, Belgium. Contact: undiet@krnic.be. Privacy: https://undiet.app/privacy · Terms: https://undiet.app/terms · Delete your account: https://undiet.app/delete-account · Support: https://undiet.app/support