Free tool · from the trials
GLP-1 weight loss by week: where should I be?
In the trials, the average participant on tirzepatide 15 mg had lost 14.8% of their starting weight by week 24 and 22.5% by week 72; on semaglutide 2.4 mg, 12.0% by week 28 and 16.9% by week 68. Averages, not a promise: some lose more, some less.
The trial and you
Example numbersBy week 24 · the SURMOUNT-1 average
196lbfrom 230 lb
- Average lost
- 14.8% · 34 lb
The average of participants while they stayed on tirzepatide (the efficacy estimand), read from the paper’s Figure 1B. An average, not a promise: some lost more, some less. Counting everyone randomized, the paper reports 20.9% at week 72.
In PepVaultPepVault’s Body tab turns your own weigh-ins into a weight trend, week by week.Where the numbers come from
Two trials won these medicines their obesity approvals, and each paper charts the average weight change at every visit. SURMOUNT-1 gave 2,539 adults tirzepatide (5, 10 or 15 mg) or placebo for 72 weeks; its Figure 1B follows participants while they stayed on treatment. STEP 1 gave 1,961 adults semaglutide 2.4 mg or placebo for 68 weeks; its Figure 1B is the observed on-treatment data.
Each point here was read from the paper’s own figure, to a tenth of a point, and checked against the numbers the papers print: SURMOUNT-1’s week-72 labels (−16.0%, −21.4%, −22.5%) and STEP 1’s −16.9% at week 68. At weeks 4 and 8 of SURMOUNT-1 the three doses were still on the same starting steps and share one marker in the figure.
Example: by week 24 of SURMOUNT-1, the average participant on tirzepatide 15 mg had lost 14.8% of their starting weight; from 230 lb, that is about 196 lb.
| Week | 15 mg | 10 mg | 5 mg |
|---|---|---|---|
| 4 | −3.2% | −3.2% | −3.2% |
| 8 | −6.0% | −6.0% | −6.0% |
| 12 | −8.4% | −8.7% | −7.9% |
| 16 | −10.6% | −11.0% | −9.2% |
| 20 | −12.6% | −12.8% | −10.5% |
| 24 | −14.8% | −14.3% | −11.7% |
| 36 | −18.4% | −17.5% | −13.7% |
| 48 | −20.6% | −19.4% | −14.9% |
| 60 | −22.0% | −20.9% | −15.9% |
| 72 | −22.5% | −21.4% | −16.0% |
| Week | 2.4 mg |
|---|---|
| 4 | −2.3% |
| 8 | −4.1% |
| 12 | −6.0% |
| 16 | −7.8% |
| 20 | −9.7% |
| 28 | −12.0% |
| 36 | −13.8% |
| 44 | −15.2% |
| 52 | −16.2% |
| 60 | −16.6% |
| 68 | −16.9% |
What an average means
The curve is the middle of a wide spread: in both trials some people lost far more and some far less, and every participant, placebo included, had counseling toward a 500-calorie daily deficit and 150 minutes of activity a week. The doses climbed in steps (tirzepatide reached its full dose at week 20, semaglutide at week 16), which is why the early weeks run close together.
Retatrutide isn’t charted: its phase 2 paper prints 17.5% at 24 weeks and 24.2% at 48 weeks on 12 mg, but its weekly figure stacks seven groups too closely to read week by week.
Questions
Do the trial averages count people who stopped the drug?
The curves follow people while they stayed on treatment. Counting everyone randomized, whether or not they kept taking it, the papers report 20.9% at week 72 on tirzepatide 15 mg (19.5% on 10 mg, 15.0% on 5 mg) and 14.9% at week 68 on semaglutide 2.4 mg.
How much did the placebo groups lose?
3.1% at week 72 in SURMOUNT-1 and 2.4% at week 68 in STEP 1, counting everyone. In both trials every participant, placebo included, had counseling toward a 500-calorie daily deficit and 150 minutes of activity a week.
What about retatrutide?
Its phase 2 trial printed 17.5% at 24 weeks and 24.2% at 48 weeks on 12 mg (least-squares means; placebo 2.1% at 48 weeks). Its week-by-week figure overlaps too closely to chart here.
Sources
- Jastreboff AM, et al. Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1). N Engl J Med 2022;387:205–216.Figure 1B, percent change in body weight by week (efficacy estimand), weeks 0 to 72, 2,539 adults with a mean starting weight of 104.8 kg; week 72 as printed in the figure. Treatment-regimen values, placebo included, from the abstract.
- Wilding JPH, et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). N Engl J Med 2021;384:989–1002.Figure 1B, body weight change from baseline by week, observed on-treatment data, weeks 0 to 68, 1,961 adults. Treatment-policy values, placebo included, from the abstract.
- Jastreboff AM, et al. Triple-hormone-receptor agonist retatrutide for obesity: a phase 2 trial. N Engl J Med 2023;389:514–526.The abstract and results: least-squares mean change in body weight at 24 and 48 weeks by dose. Its weekly figure (Figure 1A) isn’t charted here: its seven groups overlap too closely to read the 12 mg markers week by week.
Read on Oct 19, 2026.
PepVault for iPhone
Track this in PepVault
Log every dose, manage your vials, and watch your protocol come together. 7 days free on the yearly plan for new subscribers.
Choosing a tracker app? Compare peptide tracker apps