Across the GLP-1 and incretin drugs licensed for weight, average loss in the pivotal trials runs from about 8% to about 21% of body weight over roughly 12 to 18 months. The only randomised head-to-head puts a number on the gap directly: in SURMOUNT-5, 751 adults with obesity and no type 2 diabetes lost an average of 20.2% on the maximum tolerated dose of tirzepatide against 13.7% on the maximum tolerated dose of semaglutide over 72 weeks (PMID 40353578).
Any average smaller or larger than that range is usually a different question in disguise: a different dose, a shorter trial, a population with type 2 diabetes, or real-world prescribing rather than a trial. This page puts every published figure in one place with the four things that make it comparable attached.
- SURMOUNT-5 is the only randomised head-to-head: tirzepatide 20.2% against semaglutide 13.7% over 72 weeks in adults with obesity and no diabetes.
- Highest published average for a licensed drug is tirzepatide 15 mg at 20.9% over 72 weeks (SURMOUNT-1). Lowest is liraglutide 3.0 mg at 8.4 kg over 56 weeks (SCALE).
- Type 2 diabetes cuts the figure by roughly a third at the same dose for the same duration: 14.9% in STEP 1 against 9.6% in STEP 2.
- Real-world averages are lower than trial averages: 5.9% at three months and 10.9% at six months in a cohort of 175 patients.
- Retatrutide, still investigational, recorded 24.2% at 48 weeks in phase 2, the highest figure published for any of these drugs.
The one trial that compared two of them directly
Almost every weight loss percentage in circulation comes from a placebo-controlled trial, which tells you how a drug performs against nothing rather than against its competitor. Comparing two such trials is unreliable because the cohorts, the lifestyle programmes and the durations differ.
SURMOUNT-5 removed that problem for the two drugs people actually choose between. It was a phase 3b open-label trial that randomly assigned 751 adults with obesity and without type 2 diabetes to the maximum tolerated dose of tirzepatide (10 mg or 15 mg) or the maximum tolerated dose of semaglutide (1.7 mg or 2.4 mg), once weekly for 72 weeks. Average weight change was -20.2% with tirzepatide and -13.7% with semaglutide. Waist circumference fell 18.4 cm against 13.0 cm. Participants on tirzepatide were more likely to reach each of the 10%, 15%, 20% and 25% thresholds.
Two caveats belong with that result. The trial was open-label, so neither participants nor investigators were blinded, and it was funded by the manufacturer of tirzepatide. Neither undoes a 6.5 percentage point difference on a primary endpoint, but both are part of the picture.
Every published average, with its four conditions attached
A percentage is only comparable if you know the trial, the drug and dose, whether the participants had type 2 diabetes, and how long it ran. Every row below carries all four. Rows reporting kilograms report kilograms because that is what the trial measured.
| Drug and dose | Trial | Population | Duration | Average weight change |
|---|---|---|---|---|
| Retatrutide 12 mg weekly (investigational) | Phase 2 (PMID 37366315) | Obesity, no diabetes | 48 weeks | -24.2% (placebo -2.1%) |
| Tirzepatide 15 mg weekly | SURMOUNT-1 (PMID 35658024) | Overweight or obesity, no diabetes | 72 weeks | -20.9% treatment-regimen estimand |
| Tirzepatide 10 or 15 mg weekly | SURMOUNT-5 (PMID 40353578) | Obesity, no diabetes | 72 weeks | -20.2% |
| Semaglutide 2.4 mg weekly | STEP 1 (PMID 33567185) | Overweight or obesity, no diabetes | 68 weeks | -14.9% (placebo -2.4%) |
| Semaglutide 1.7 or 2.4 mg weekly | SURMOUNT-5 (PMID 40353578) | Obesity, no diabetes | 72 weeks | -13.7% |
| Semaglutide tablets 25 mg daily | OASIS 4 (PMID 40934115) | Overweight or obesity, no diabetes | 64 weeks | -13.6% (placebo -2.2%) |
| Semaglutide 2.4 mg weekly | STEP 2 (PMID 33667417) | Overweight or obesity with type 2 diabetes | 68 weeks | -9.6% (placebo -3.4%) |
| Liraglutide 3.0 mg daily | SCALE (PMID 26132939) | Overweight or obesity, no diabetes | 56 weeks | -8.4 kg from a mean 106.2 kg, about 8% |
| Semaglutide 2.0 mg weekly | SUSTAIN FORTE (PMID 34293304) | Type 2 diabetes | 40 weeks | -6.9 kg |
The ordering is the useful part. The two drugs at the top act on more than one receptor: retatrutide on three (GIP, GLP-1 and glucagon) and tirzepatide on two (GIP and GLP-1). Everything below them is a pure GLP-1 receptor agonist. The mechanism tracks the ranking closely enough that it is the best available explanation for it, though no trial has isolated the GIP contribution in humans.
The bottom two rows are not failures
SUSTAIN FORTE tested semaglutide 2.0 mg, which is the maximum Ozempic dose, in people with type 2 diabetes over 40 weeks, with weight as a secondary outcome rather than the point of the trial. Its 6.9 kg is a smaller number than STEP 1 for three separate reasons at once: a lower dose, a shorter trial and a harder population. It is not a measurement of the same thing.
This is the single most common error in GLP-1 content, and it runs in the other direction too. The 14.9% figure belongs to semaglutide 2.4 mg, a Wegovy dose that Ozempic cannot reach, and attributing it to Ozempic overstates that product by a wide margin. We cover each drug separately for this reason: Wegovy, Ozempic, Zepbound and Mounjaro.
Type 2 diabetes moves the number more than anything else
STEP 1 and STEP 2 are the cleanest comparison available on this point, because they used the same drug at the same dose for the same 68 weeks and differed mainly in whether participants had type 2 diabetes. The results were 14.9% and 9.6%, a drop of about a third.
Real-world data reproduces the split. In a retrospective cohort of 175 patients prescribed semaglutide for weight loss, six-month loss averaged 11.8% for people without type 2 diabetes and 7.2% for people with it (PMID 36121652). The gap is consistent enough that any average quoted without a diabetes status should be treated as the more optimistic of the two possibilities.
What the average looks like month by month
None of the trials above publishes a monthly curve, so a per-month figure has to come from cohorts that measured earlier. The same 175-patient cohort recorded 5.9% at three months and 10.9% at six months.
| Period | Cumulative average loss | Implied rate in that period |
|---|---|---|
| Months 1 to 3 | 5.9% | About 2.0% of body weight a month |
| Months 4 to 6 | 10.9% | About 1.7% a month |
| Through month 15 or 16 | 14.9% (STEP 1, semaglutide 2.4 mg) | Under 0.5% a month over the remainder |
The shape matters more than any single row. Loss is front-loaded, the rate falls as the months pass, and the curve flattens well before treatment stops. Someone four months in and someone fourteen months in are not on the same part of the curve, which is why comparing your own progress against a trial endpoint is misleading until you have been on a maintenance dose for a while. What happens when the curve flattens for good is covered in our piece on the GLP-1 weight loss plateau.
Why SURMOUNT-1 has two different numbers
You will see tirzepatide 15 mg quoted as both 20.9% and 22.5%. Both come from SURMOUNT-1 and both are correct. They are two estimands, which are two different questions asked of the same data.
- The treatment-regimen estimand, 20.9%, counts everyone randomised, including people who stopped the drug, and is the more conservative figure. It answers what happens if a population is put on this treatment.
- The efficacy estimand, 22.5%, estimates what would have happened if everyone had stayed on treatment throughout. It answers what the drug does when taken as intended.
The same distinction applies to the other trials, and it is one reason two honest sources can differ by one or two percentage points on the same drug. The gap between the two is also a rough measure of how many people stopped, which is information in its own right.
Why your own number will differ from all of these
In STEP 1, half the semaglutide group lost 15% or more while roughly one in seven did not reach 5%, on the same dose for the same duration. An average is the middle of a wide distribution, not a prediction. The factors that move an individual within that distribution are well documented:
- Diabetes status, worth several percentage points at every time point measured.
- The dose actually reached. Trial averages assume escalation to the maintenance dose. Stopping at a lower step for tolerability means sitting lower on the curve.
- Time on treatment, given how front-loaded the curve is.
- Starting weight, which decides what a percentage is worth in pounds. 15% is 27 lb at 180 lb and 45 lb at 300 lb.
- The lifestyle programme. Every trial here paired the drug with structured diet and activity counselling in both the drug and placebo arms, and the placebo arms still lost 2% to 3%.
Turn a percentage into your own pound figure
See what each trial average works out to from your starting weight, week by week.
The most useful thing you can do with the table above is stop reading it as percentages. Running your own starting weight through the GLP-1 weight loss calculator converts each trial average into pounds and a week-by-week shape, which is a more honest reference point than a population figure. For the drugs sold as vials rather than pens, our mg to units explainer covers the arithmetic that goes with them.
FAQ
What is the average weight loss on a GLP-1?
Between about 8% and about 21% of body weight in the pivotal trials, over 12 to 18 months. Tirzepatide 15 mg recorded 20.9% over 72 weeks in SURMOUNT-1, semaglutide 2.4 mg recorded 14.9% over 68 weeks in STEP 1, and liraglutide 3.0 mg recorded 8.4 kg over 56 weeks in SCALE. Averages in people with type 2 diabetes are roughly a third lower at the same dose.
Which GLP-1 produces the most weight loss?
Among licensed drugs, tirzepatide. The only randomised head-to-head, SURMOUNT-5, recorded 20.2% with tirzepatide against 13.7% with semaglutide over 72 weeks in adults with obesity and no diabetes. Retatrutide recorded 24.2% at 48 weeks in phase 2 but is still investigational and not licensed.
How much weight can you lose on a GLP-1 in a month?
Early loss is faster than later loss. A real-world cohort of 175 patients averaged 5.9% at three months, which is about 2% of body weight a month, then 10.9% at six months, which is about 1.7% a month across the second three. Over the full 68 weeks of STEP 1 the overall rate works out below 1% a month.
Why are real-world results lower than trial results?
Three reasons. Trial participants are escalated to and held at a maintenance dose, they receive structured diet and activity counselling as part of the protocol, and the cohorts are selected by eligibility criteria. Real-world prescribing involves a wider range of doses, more interruptions and less support.
Does the same percentage mean the same weight loss for everyone?
No. A percentage of body weight translates into very different pound figures: 15% is about 27 lb from 180 lb and about 45 lb from 300 lb. Within the trials the spread is also wide, with half the STEP 1 semaglutide group losing 15% or more and roughly one in seven not reaching 5%.
Is a GLP-1 taken as a tablet less effective?
Not necessarily. OASIS 4 tested semaglutide tablets at 25 mg once daily in adults with overweight or obesity and no diabetes and recorded 13.6% at week 64, close to the 14.9% that injected semaglutide 2.4 mg recorded over 68 weeks in STEP 1. They are separate trials rather than a head-to-head, so the comparison is indicative rather than conclusive.
This article is for information only and is not medical advice. Trial averages describe populations, not individuals, and nothing here is a prediction of your own result. Treatment decisions belong with your prescriber.
Sources
- Aronne LJ, Horn DB, le Roux CW, et al. Tirzepatide as Compared with Semaglutide for the Treatment of Obesity (SURMOUNT-5). <em>N Engl J Med</em>. 2025;393(1):26-36. PMID: 40353578
- Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). <em>N Engl J Med</em>. 2022;387(3):205-216. PMID: 35658024
- Wilding JPH, Batterham RL, Calanna S, et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1). <em>N Engl J Med</em>. 2021;384(11):989-1002. PMID: 33567185
- Davies M, Féderèr Hansen K, Lingvay I, et al. Semaglutide 2.4 mg once a week in adults with overweight or obesity, and type 2 diabetes (STEP 2). <em>Lancet</em>. 2021;397(10278):971-984. PMID: 33667417
- Frias JP, Auerbach P, Bajaj HS, et al. Efficacy and safety of once-weekly semaglutide 2.0 mg versus 1.0 mg in patients with type 2 diabetes (SUSTAIN FORTE). <em>Lancet Diabetes Endocrinol</em>. 2021;9(9):563-574. PMID: 34293304
- Jastreboff AM, Kaplan LM, Frias JP, et al. Triple-Hormone-Receptor Agonist Retatrutide for Obesity: A Phase 2 Trial. <em>N Engl J Med</em>. 2023;389(6):514-526. PMID: 37366315
- Wharton S, Lingvay I, Bogdanski P, et al. Oral Semaglutide at a Dose of 25 mg in Adults with Overweight or Obesity (OASIS 4). <em>N Engl J Med</em>. 2025;393(11):1077-1087. PMID: 40934115
- Pi-Sunyer X, Astrup A, Fujioka K, et al. A Randomized, Controlled Trial of 3.0 mg of Liraglutide in Weight Management (SCALE). <em>N Engl J Med</em>. 2015;373(1):11-22. PMID: 26132939
- Ghusn W, De la Rosa A, Sacoto D, et al. Weight Loss Outcomes Associated With Semaglutide Treatment for Patients With Overweight or Obesity. <em>JAMA Netw Open</em>. 2022;5(9):e2231982. PMID: 36121652