GLP-1 Plateau: Why Weight Loss Stalls on Wegovy and Zepbound

If your weight has stopped dropping on semaglutide (Wegovy) or tirzepatide (Zepbound, Mounjaro), the research says this is a normal part of treatment. In a post hoc analysis of the SURMOUNT-1 and SURMOUNT-4 trials, researchers defined a plateau as a weight change under 5% over a 12-week interval and every 12-week interval after that ^[1]. By that definition, the median time to plateau in SURMOUNT-1 ranged from 24.3 weeks to 36.1 weeks depending on starting BMI category, and by week 72, roughly 88% to 90% of participants had reached a plateau ^[1].

The plateau is the transition point where the body shifts from an active weight-loss phase into a weight-maintenance phase ^[1]. Withdrawal trials show what happens on each path: in STEP 4 and SURMOUNT-4, participants were randomized at a fixed time point — week 20 and week 36, respectively, regardless of how much weight they had lost — to continue the drug or switch to placebo. Those who continued lost more weight, while those switched to placebo regained ^[5][6].

How do researchers define a weight-loss plateau?

In a 2025 post hoc analysis of the SURMOUNT-1 and SURMOUNT-4 tirzepatide trials, Horn and colleagues called it a plateau when a participant’s weight changed by less than 5% over a 12-week interval, and by less than 5% over every 12-week interval that followed ^[1]. Time to plateau was counted from randomization to the start of the first such 12-week interval ^[1].

The analysis included only participants who stayed adherent to tirzepatide and had lost at least 5% of their body weight by the trial’s primary endpoint — 1,438 participants in SURMOUNT-1 and 259 in SURMOUNT-4 ^[1]. The researchers frame obesity treatment as having two phases: an initial weight-loss phase, then a weight-maintenance phase, with the plateau as the transition between them ^[1].

When does the plateau usually happen on tirzepatide?

In SURMOUNT-1, the median time to plateau varied by starting BMI category, with people who started heavier reaching their plateau later ^[1]:

Starting BMI category	Median time to plateau	At plateau by week 72
Overweight	24.3 weeks	90.2%
Class I obesity	26.0 weeks	88.9%
Class II obesity	36.1 weeks	87.6%
Class III obesity	36.1 weeks	87.8%

The difference between class II or III obesity and the overweight group was statistically significant (p < .05) ^[1]. Results in SURMOUNT-4 were similar ^[1]. These are medians among adherent trial participants who lost at least 5% of their weight, so they describe the trial population rather than predict any one person’s timeline ^[1].

A later plateau was associated with the 10 mg and 15 mg doses, younger age, and female sex, while BMI and waist circumference showed no association once other factors were accounted for ^[1]. A longer time to plateau was generally associated with greater total weight reduction ^[1].

What do the semaglutide trials show?

In STEP 1, 1,961 adults with overweight or obesity took semaglutide 2.4 mg weekly or placebo for 68 weeks; mean weight change was -14.9% with semaglutide versus -2.4% with placebo ^[2]. Dose escalation started at 0.25 mg weekly and increased every 4 weeks, reaching the 2.4 mg maintenance dose by week 16 ^[2].

STEP 5 ran for 104 weeks in 304 participants and reported a mean change of -15.2% with semaglutide versus -2.6% with placebo, described as sustained weight loss over the full two years ^[3].

Why does weight loss stall on a GLP-1?

The body pushes back as weight comes off, through two adaptations described in the plateau analysis ^[1]. The first is hormonal: ghrelin, a hunger hormone, rises, and satiety hormones fall as weight is lost. The second is metabolic: energy expenditure decreases, and the body’s energy balance shifts from negative (burning more than taken in) to neutral ^[1].

Weight response and time to plateau also vary from person to person, and the analysis lists genetics, age, other medications a person takes, and the type of weight-loss intervention as factors that can influence the timing ^[1].

What do the withdrawal trials show about continuing versus stopping?

Two withdrawal trials randomized participants at a set time point — not at a plateau — to either continue the drug or switch to placebo.

In STEP 4, 803 adults completed a 20-week run-in on semaglutide 2.4 mg with a mean weight loss of 10.6%, and were then randomized 2:1 — regardless of how much weight they had lost — to continue semaglutide or switch to placebo for 48 more weeks ^[5][8]. From week 20 to week 68, those who continued lost another 7.9% on average, while those switched to placebo gained 6.9% ^[5].

SURMOUNT-4 followed a similar design with tirzepatide. After a 36-week open-label lead-in at the maximum tolerated dose of 10 or 15 mg, during which participants lost a mean of 20.9%, 670 were randomized to continue tirzepatide or switch to placebo for 52 weeks ^[6]. From week 36 to week 88, the tirzepatide group lost another 5.5% while the placebo group regained 14.0% ^[6]. From week 0 to week 88, the totals were -25.3% for continued tirzepatide versus -9.9% for the withdrawn group ^[6].

At week 88, 89.5% of those still on tirzepatide had kept at least 80% of the weight they lost during the lead-in, compared with 16.6% of those switched to placebo ^[6].

Is a slow start the same as a plateau?

No, and the research draws a clear line between the two. A post hoc analysis of SURMOUNT-1 looked at 1,545 tirzepatide-treated participants and found 278 (18%) were “late responders” — they had lost less than 5% of their weight at week 12 ^[7]. These late responders were more often male (45% vs. 30%) and heavier at baseline (110.2 vs. 103.6 kg) than early responders ^[7].

Among those late responders, 70% reached at least 5% weight loss by week 24, the end of dose titration, and 90% reached it by week 72. Their mean time to a 5% loss was 24.8 weeks ^[7]. The analysis notes that titration to the maximum dose may take up to 20 weeks, so a slow first 12 weeks can simply reflect a person still climbing the dose ladder ^[7].

STEP 4 told a similar story for semaglutide. Being a responder at week 20 strongly predicted reaching at least 5% loss by week 68 (positive predictive value 96.4%), but being a non-responder at week 20 was a weak predictor of failure (negative predictive value 42.9%) ^[8]. Week-20 non-responders who continued semaglutide lost a mean of 6.4% from week 0 to week 68, versus -0.3% for those switched to placebo ^[8].

Does a higher dose push the plateau later?

In the SURMOUNT-1 and SURMOUNT-4 analysis, participants on the higher tirzepatide doses (10 mg and 15 mg) reached their plateau later than those on lower doses ^[1]. Whether raising a dose helps any individual is a decision for a prescriber, and the trial data describe group averages, not a rule for dose changes.

The approved dosing schedules show how long the climb to a full dose takes. Wegovy injection starts at 0.25 mg weekly for 4 weeks and titrates every 4 weeks, with 2.4 mg weekly as the usual maintenance dose ^[9]. The Wegovy label states that for patients who tolerate 2.4 mg for at least 4 weeks and for whom additional weight reduction is clinically indicated, the dose may be increased to a maximum of 7.2 mg weekly ^[9]. In the label’s Study 8 in patients with obesity, mean weight change at week 72 was -18.8% on 7.2 mg versus -15.5% on 2.4 mg and -3.9% on placebo ^[9].

Zepbound starts at 2.5 mg weekly for 4 weeks, then increases in 2.5 mg increments after at least 4 weeks at each step, with maintenance doses of 5, 10, or 15 mg and a maximum of 15 mg ^[4].

Do real-world patients plateau like trial participants?

Real-world results tend to be smaller than trial results, and one reason is that many people are on lower doses or stop early. A retrospective study of electronic health records from a health system in Ohio and Florida followed 7,881 adults who started injectable semaglutide (6,109) or tirzepatide (1,772) between 2021 and 2023 ^[10]. Of these, 80.8% were on low maintenance dosages ^[10].

Mean weight loss at one year was 8.7% overall. It was 11.9% among those with no discontinuation, 6.8% among those with late discontinuation, and 3.6% among those who discontinued within three months ^[10]. Factors associated with achieving at least 10% loss at one year included not discontinuing the medication, tirzepatide versus semaglutide, a higher dosage, and female sex ^[10]. As an observational cohort, this study shows associations rather than causes ^[10].

Does exercise help with maintaining weight loss?

The S-LITE trial tested exercise as a maintenance strategy, though it used daily liraglutide 3.0 mg — a different GLP-1 medication from semaglutide or tirzepatide — after an 8-week low-calorie diet. The 195 participants lost a mean of 13.1 kg on the diet, then were randomized for one year to exercise, liraglutide, both, or placebo ^[11].

Compared with placebo at one year, the exercise group kept off 4.1 kg more, the liraglutide group 6.8 kg more, and the combination group 9.5 kg more ^[11]. The combination also cut body-fat percentage by 3.9 percentage points, roughly double the effect of exercise alone (-1.7) or liraglutide alone (-1.9), and it was the only strategy associated with improvements in HbA1c, insulin sensitivity, and cardiorespiratory fitness ^[11].

What happens if the medication is stopped?

The withdrawal data are consistent across both drugs: most people regain a large share of what they lost.

In the STEP 1 extension, 327 participants were followed for a year after stopping semaglutide and the structured lifestyle program at week 68. They had lost a mean of 17.3% during treatment, then regained 11.6 percentage points by week 120, leaving a net loss of 5.6% ^[16]. At week 120, 48.2% were still at least 5% below their baseline weight, and most cardiometabolic improvements had reverted toward baseline ^[16].

In a post hoc analysis of SURMOUNT-4 covering 308 participants who stopped tirzepatide, 82.5% regained at least 25% of the weight they had lost during the 36-week lead-in by week 88 ^[17]. Greater regain was associated with greater reversal of improvements in waist circumference, blood pressure, non-HDL cholesterol, glycemic measures, and insulin resistance ^[17].

What did body composition look like after 72 weeks of tirzepatide?

A DXA substudy of SURMOUNT-1 measured body composition from baseline to week 72 in 160 participants. With tirzepatide, body weight changed -21.3%, fat mass -33.9%, and lean mass -10.9% ^[18]. About 75% of the weight lost was fat mass and 25% was lean mass, a pattern seen in both the tirzepatide and placebo groups ^[18].

How do tirzepatide and semaglutide compare on total weight loss?

In SURMOUNT-5, 751 adults with obesity but no type 2 diabetes were treated open-label for 72 weeks with the maximum tolerated dose of tirzepatide (10 or 15 mg) or semaglutide (1.7 or 2.4 mg). Mean weight change was -20.2% with tirzepatide versus -13.7% with semaglutide, and waist circumference fell 18.4 cm versus 13.0 cm ^[13].

A 2026 meta-analysis by Paccola and colleagues pooled 10 head-to-head studies — randomized trials plus observational studies — totaling 41,381 participants, and found tirzepatide associated with 4.28 percentage points greater weight loss than semaglutide. The same analysis found serious adverse events more frequent with tirzepatide (relative risk 1.83) ^[14].

Sources

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