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Tool · Trial results by week

GLP-1 results by week.

How much weight did people lose on semaglutide or tirzepatide by each week of the trials?

In STEP 1, people on semaglutide 2.4 mg lost 14.9% of their body weight on average by week 68, against 2.4% on placebo. In SURMOUNT-1, people on tirzepatide lost 15.0% to 20.9% by week 72, depending on dose, against 3.1% on placebo. These are trial averages, not predictions for you.

Updated

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Medicine and trial
STEP 1 · 2.4 mg · week 68−15.6%Average change in body weight from the start of the trial, on semaglutide 2.4 mg.
Placebo · week 68−2.8%Average change with placebo injections, alongside the same diet and activity advice.

Week 68: these are the values printed on the label figure.

Week 680%-5%-10%-15%-20%-25%Week 081628446068

What the trial published. −14.9% with semaglutide 2.4 mg and −2.4% with placebo at week 68 (treatment-policy estimate). Wilding et al., New England Journal of Medicine, 2021 (abstract).

Where the weekly values come from. WEGOVY US prescribing information, Figure 7 (STEP 1), observed mean, in-trial. US prescribing information on DailyMed. The label figure and the paper use different analyses, so their final numbers differ slightly.

Average results from clinical trials, not a prediction for you. Trial participants were 1,961 adults with obesity or overweight, without diabetes, with diet and activity counselling. Individual results varied widely around these averages.

Read this first

Average results from clinical trials, not a prediction for you.

An average hides a wide spread. In STEP 1, the standard deviation of weight change on semaglutide was about 10 percentage points, so many people lost much more or much less than the average.

Trial participants followed a fixed dose schedule and had regular diet and activity counselling. Doses, timing and health conditions differ in everyday care.

The “Stopping vs staying on” view comes from trials where everyone took the drug first and was then randomly assigned to keep taking it or switch to placebo. Only people who reached the trial’s dose during the lead-in were randomised: 2.4 mg in STEP 4, and their maximum tolerated dose of 10 mg or 15 mg in SURMOUNT-4. That depended on reaching the dose, not on how much weight they had lost. So the view shows what happened on average to people who reached that dose, not to everyone who starts the drug. More on stopping is on GLP-1 by the numbers. The dose steps from each label are in titration schedules.

Method

How this works.

Inputs

You choose a view, a medicine or two curves, a dose where the trial tested more than one, and a week. Nothing about you is entered or stored.

Data

Average % change in body weight at each week the trial figure plots, read off the published figures in the US prescribing information: STEP 1 (Wegovy label, Figure 7), SURMOUNT-1 (Zepbound label, Figure 3), STEP 4 (Wegovy label, Figure 8) and SURMOUNT-4 (Zepbound label, Figure 5).

For SURMOUNT-1, STEP 4 and SURMOUNT-4, each marker was located by fitting its shape against the figure image, with the axes calibrated from the tick marks. A point is shown only if two uncertainty checks are both within 0.25 percentage points; otherwise it says “Not readable from the published figure”. STEP 1 was read earlier (15 October 2026) from the marker centres. Where a figure prints a number, that number is shown; against those printed numbers, every reading is within 0.07 points.

Formula

None. Values are shown as read, to one decimal place. Weeks the figure doesn’t plot are left out, not filled in. The compare view shows a gap only when both curves come from the same randomised trial. A gap no bigger than the two readings’ combined error (up to 0.25 points for each value read from a figure, none for a printed value), or at a week where the markers overlap, is shown as “No clear gap”.

Sources
  • WEGOVY US prescribing information, revised June 2026 (STEP 1 and STEP 4 figures).
  • ZEPBOUND US prescribing information, revised August 2026 (SURMOUNT-1 and SURMOUNT-4 figures).
  • Published results: STEP 1 (NEJM, 2021), STEP 4 (JAMA, 2021), SURMOUNT-1 (NEJM, 2022), SURMOUNT-4 (JAMA, 2024) and SURMOUNT-5 (ClinicalTrials.gov results).
  • Read on: STEP 1, 15 October 2026; SURMOUNT-1 (re-read), STEP 4 and SURMOUNT-4, 26 October 2026.
Limits

Averages hide a wide spread: in STEP 1 the standard deviation was about 10 percentage points. Figures show observed means, which differ slightly from the papers’ headline estimates. The withdrawal trials only randomised people who reached the trial’s dose (2.4 mg in STEP 4; a maximum tolerated dose of 10 mg or 15 mg in SURMOUNT-4), so their curves leave out people who stopped early or didn’t reach it. Different trials enrolled different people for different lengths of time.

What this is not

Not a prediction of your result, not advice to start, stop or change a medicine or dose, and not a ranking of medicines. Talk to your prescriber about your own treatment.

Sources

  1. Wilding et al., Once-weekly semaglutide in adults with overweight or obesity (STEP 1), New England Journal of Medicine, 2021Published week 68 results: −14.9% vs −2.4% (treatment-policy estimate).
  2. WEGOVY (semaglutide) US prescribing information, Figure 7, DailyMedWeekly STEP 1 values digitised from this figure; the figure prints −15.6% and −2.8% at week 68.
  3. Jastreboff et al., Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1), New England Journal of Medicine, 2022Published week 72 results: −15.0%, −19.5%, −20.9% vs −3.1% (treatment-regimen estimate).
  4. ZEPBOUND (tirzepatide) US prescribing information, Figure 3, DailyMedWeekly SURMOUNT-1 values digitised from this figure, one dose marker at a time; the figure prints −16.1%, −20.9%, −22.0% and −3.3% at week 72. At week 8 the 10 mg marker is hidden behind the others, so it is not readable from the published figure.
  5. ClinicalTrials.gov NCT03548935 results (STEP 1)Observed week 68 change −15.6% (SD 10.1) on semaglutide, −2.8% (SD 6.5) on placebo.
  6. Rubino et al., Effect of continued weekly subcutaneous semaglutide vs placebo on weight loss maintenance (STEP 4), JAMA, 2021Run-in −10.6%; week 20 to 68: −7.9% continued vs +6.9% switched to placebo (treatment-policy estimate).
  7. WEGOVY (semaglutide) US prescribing information, Figure 8 (right panel, Study 5 = STEP 4), DailyMed, revised June 2026Weekly STEP 4 values digitised from this figure on 26 October 2026; it prints −17.7% (continued) and −5.4% (placebo) at week 68.
  8. Aronne et al., Continued treatment with tirzepatide for maintenance of weight reduction (SURMOUNT-4), JAMA, 2024Lead-in −20.9%; week 36 to 88: −5.5% continued vs +14.0% switched to placebo (treatment-regimen estimate).
  9. ZEPBOUND (tirzepatide) US prescribing information, Figure 5 (Study 4 = SURMOUNT-4), DailyMed, revised August 2026Weekly SURMOUNT-4 values digitised from this figure on 26 October 2026; it prints −20.9% at week 36, and −25.8% (continued) and −9.5% (placebo) at week 88.
  10. ClinicalTrials.gov NCT05822830 results (SURMOUNT-5, tirzepatide vs semaglutide)Week 72: −20.2% tirzepatide vs −13.7% semaglutide (least-squares means).
  11. Download the digitised curves (CSV)STEP 4 and SURMOUNT-4 label-figure rows are STEP4_label and SURMOUNT4_label. Published endpoints are in trial_weight_endpoints.csv; residuals in trial_weight_curves_validation.csv.

This tool shows published trial averages. It doesn’t give medical advice or predict anyone’s result. Talk to your prescriber about your own treatment.