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How GLP-1 weight loss unfolds over time: what the trials show

Updated Sep 27, 2026. Numbers in brackets link to the source each fact comes from.

In the big trials, most of the weight came off in roughly the first year to year and a half, and then weight held steady for as long as the trials followed people who kept taking the medicine [9]. When people stopped, most of them regained a large share of what they had lost. The trials report averages, so any one person’s curve can look quite different.

The first months: dose escalation

Nobody starts at the full dose. Wegovy starts at 0.25 mg a week for the first four weeks [21] and reaches its maintenance dose from week 17 [1]. Zepbound starts at 2.5 mg, moves to 5 mg after four weeks, and can rise in 2.5 mg steps at least four weeks apart [2]. In the main Zepbound trial, the dose-escalation period lasted up to 20 weeks [7].

Weight loss is already under way during this period. Two trials that gave everyone the drug before splitting them into groups show how much:

  • In STEP 4, people who finished a 20-week run-in on semaglutide had lost 10.6% of their weight on average [3].
  • In SURMOUNT-4, people who finished a 36-week lead-in on tirzepatide had lost 20.9% on average [4].

Both figures count only people who stayed on the drug long enough to be randomized. The Wegovy label warns that results from its run-in trial may not reflect what happens to people starting the medicine in general, since those who stopped early or could not reach the full dose were left out [17]. In the Zepbound withdrawal trial, 14.4% of people stopped before week 36, most often because of side effects [19].

Where the main trials ended up

Trial Medicine and dose Average weight change Placebo
STEP 1, 68 weeks Semaglutide 2.4 mg -14.9% [5] -2.4% [5]
SURMOUNT-1, 72 weeks Tirzepatide 5 mg -15.0% [6] -3.1% [6]
SURMOUNT-1, 72 weeks Tirzepatide 10 mg -19.5% [6] -3.1% [6]
SURMOUNT-1, 72 weeks Tirzepatide 15 mg -20.9% [6] -3.1% [6]

Each trial had its own people and design, so compare within a row, not across medicines. The label-by-label figures are on our weight loss results page.

The plateau

Trials that ran longer show weight leveling off rather than falling forever:

  • SELECT, semaglutide. Weight loss continued through about 65 weeks and then held for up to 4 years; at 208 weeks the average reduction was 10.2% [9]. SELECT enrolled people with heart disease, not a weight-loss-only group.
  • STEP 5, semaglutide. At two years, the average change was -15.2%, against -2.6% on placebo [8].
  • SURMOUNT-1, three years. Among participants with obesity and prediabetes who stayed on their assigned dose for 176 weeks [11], average loss was 12.3%, 18.7% and 19.7% on the 5, 10 and 15 mg doses [10].

In these trials, a slowdown after the first year was the usual pattern. Whether a slowdown in your own case means you need a dose change is a question for your prescriber, who can check it against the label’s dosing steps.

What happens when people stop

Both withdrawal trials switched some participants to placebo after the early weight loss, and both labels include the result [17] [18].

  • Semaglutide (STEP 4). From week 20 to week 68, people who kept taking semaglutide lost another 7.9%, while those switched to placebo gained 6.9% [12].
  • Tirzepatide (SURMOUNT-4). From week 36 to week 88, people who stayed on tirzepatide lost another 5.5%, while those switched to placebo regained 14.0% [13]. Over the whole 88 weeks, the placebo group ended 9.9% below their starting weight, against 25.3% for those who stayed on the drug [14]. The Zepbound label reports that continuing treatment led to significantly more weight reduction than switching to placebo [18].
  • After stopping everything (STEP 1 extension). One year after semaglutide and the lifestyle program ended, participants had regained about two-thirds of the weight they had lost [16]. By week 120, their net loss was 5.6% [15].

The labels describe these medicines as treatment to reduce weight and maintain the reduction long term [20]. They do not set a date to stop.

Using this timeline

  • Early weeks are for building up the dose. The Zepbound label says most nausea, vomiting and diarrhea happened during dose escalation and eased over time [22].
  • Most of the loss in these trials happened in the first year to year and a half, then weight held steady.
  • Stopping was followed by regain in both withdrawal trials.

Do not change your dose or stop on your own. If your weight has stopped moving or you are thinking about stopping, talk to your prescriber first.

Sources

  1. Maintenance Dosage 17 and onward See the indication below for the recommended maintenance dosage(s) dailymed.nlm.nih.gov, read Sep 27, 2026.
  2. After 4 weeks, increase the dosage to 5 mg injected subcutaneously once weekly. The dosage may be increased in 2.5 mg increments, after at least 4 weeks on the current dose dailymed.nlm.nih.gov, read Sep 27, 2026.
  3. Among 803 study participants who completed the 20-week run-in period (with a mean weight loss of 10.6%) pubmed.ncbi.nlm.nih.gov, read Sep 27, 2026.
  4. Participants (n = 670; mean age, 48 years; 473 [71%] women; mean weight, 107.3 kg) who completed the 36-week lead-in period experienced a mean weight reduction of 20.9%. pubmed.ncbi.nlm.nih.gov, read Sep 27, 2026.
  5. The mean change in body weight from baseline to week 68 was -14.9% in the semaglutide group as compared with -2.4% with placebo pubmed.ncbi.nlm.nih.gov, read Sep 27, 2026.
  6. The mean percentage change in weight at week 72 was -15.0% (95% confidence interval [CI], -15.9 to -14.2) with 5-mg weekly doses of tirzepatide, -19.5% (95% CI, -20.4 to -18.5) with 10-mg doses, and -20.9% (95% CI, -21.8 to -19.9) with 15-mg doses and -3.1% (95% CI, -4.3 to -1.9) with placebo pubmed.ncbi.nlm.nih.gov, read Sep 27, 2026.
  7. for 72 weeks, including a 20-week dose-escalation period. pubmed.ncbi.nlm.nih.gov, read Sep 27, 2026.
  8. The mean change in body weight from baseline to week 104 was -15.2% in the semaglutide group (n = 152) versus -2.6% with placebo (n = 152) pubmed.ncbi.nlm.nih.gov, read Sep 27, 2026.
  9. In patients treated with semaglutide, weight loss continued over 65 weeks and was sustained for up to 4 years. At 208 weeks, semaglutide was associated with mean reduction in weight (-10.2%) pubmed.ncbi.nlm.nih.gov, read Sep 27, 2026.
  10. At 176 weeks, the mean percent change in body weight among the participants who received tirzepatide was -12.3% with the 5-mg dose, -18.7% with the 10-mg dose, and -19.7% with the 15-mg dose, as compared with -1.3% among those who received placebo pubmed.ncbi.nlm.nih.gov, read Sep 27, 2026.
  11. The current analysis involved the participants with both obesity and prediabetes, who received their assigned dose of tirzepatide or placebo for a total of 176 weeks pubmed.ncbi.nlm.nih.gov, read Sep 27, 2026.
  12. With continued semaglutide, mean body weight change from week 20 to week 68 was -7.9% vs +6.9% with the switch to placebo pubmed.ncbi.nlm.nih.gov, read Sep 27, 2026.
  13. The mean percent weight change from week 36 to week 88 was -5.5% with tirzepatide vs 14.0% with placebo pubmed.ncbi.nlm.nih.gov, read Sep 27, 2026.
  14. The overall mean weight reduction from week 0 to 88 was 25.3% for tirzepatide and 9.9% for placebo. pubmed.ncbi.nlm.nih.gov, read Sep 27, 2026.
  15. Following treatment withdrawal, semaglutide and placebo participants regained 11.6 (SD: 7.7) and 1.9 (SD: 4.8) percentage points of lost weight, respectively, by week 120, resulting in net losses of 5.6% (SD: 8.9%) and 0.1% (SD: 5.8%), respectively, from week 0 to week 120. pubmed.ncbi.nlm.nih.gov, read Sep 27, 2026.
  16. One year after withdrawal of once-weekly subcutaneous semaglutide 2.4 mg and lifestyle intervention, participants regained two-thirds of their prior weight loss, with similar changes in cardiometabolic variables. pubmed.ncbi.nlm.nih.gov, read Sep 27, 2026.
  17. Because patients who discontinued WEGOVY injection during titration and those who did not reach the 2.4 mg weekly dose were not eligible for the randomized-treatment period, the results may not reflect the experience of patients in the general population who are first starting WEGOVY injection. dailymed.nlm.nih.gov, read Sep 27, 2026.
  18. After weight loss with ZEPBOUND treatment during the open-label lead-in period (Week 0 to Week 36), continued treatment with ZEPBOUND from randomization (Week 36) to Week 88 resulted in a statistically significant reduction in body weight compared with placebo dailymed.nlm.nih.gov, read Sep 27, 2026.
  19. Of the 783 patients who started ZEPBOUND at Week 0, 14.4% discontinued treatment before randomization at Week 36, and adverse events were the most common reason for discontinuation (6.8%). dailymed.nlm.nih.gov, read Sep 27, 2026.
  20. to reduce excess body weight and maintain weight reduction long term in: dailymed.nlm.nih.gov, read Sep 27, 2026.
  21. Starting Dosage 1 through 4 0.25 mg dailymed.nlm.nih.gov, read Sep 27, 2026.
  22. The majority of nausea, vomiting, and/or diarrhea events occurred during dose escalation and decreased over time. dailymed.nlm.nih.gov, read Sep 27, 2026.

This page reports what official sources say; it is not medical advice. Medical disclaimer.