Weight plateaus on a GLP-1

Why weight levels off

Body weight settles when energy in and energy out come back into balance. A 2024 study by a researcher at the NIDDK used a validated mathematical model of metabolism to ask why different treatments run for different lengths of time before levelling off. In the model, each treatment has two parts: a lasting shift away from the starting weight, and a feedback loop in which appetite rises as weight falls ^[6].

The model found that GLP-1 medicines and gastric bypass weakened that appetite loop, while dieting alone did not, which is why weight kept falling for longer before the plateau ^[6]. The authors call the results preliminary, and a model of group averages cannot explain one person’s scale. It does offer a plain reading of a plateau: a new balance point, not necessarily a medicine that has stopped working.

When most of the change happens

According to the NIDDK, an institute of the US National Institutes of Health, the bulk of the weight lost on prescription weight-management medicines comes in the first 6 months after starting ^[7]. Doses also climb at the start. The Zepbound® label begins with a 2.5 mg dose that is meant for starting treatment rather than for maintenance and spaces each later increase by a minimum of 4 weeks ^[8]. In SURMOUNT-1, the escalation period took the first 20 weeks ^[4].

The Zepbound® and Wegovy® labels both ask prescribers to choose the maintenance dose with treatment response and tolerability in mind ^[8][9]. A slower phase after the early months fits that general picture; it does not by itself mean a dose change is needed.

Semaglutide (Wegovy®) over time

STEP 1 followed 1,961 adults without diabetes on weekly semaglutide 2.4 mg or placebo for 68 weeks, both with lifestyle support. Average weight changed by −14.9% against −2.4%, and the spread was wide: 86.4% of people on semaglutide lost at least 5%, 69.1% at least 10% and 50.5% at least 15% ^[12].

STEP 5 ran for two years in 304 adults. At week 104 the average change was −15.2% against −2.6% on placebo ^[2]. The European product information describes the shape: weight fell to week 68 and then plateaued, while the placebo group lost less and levelled off at about week 20 ^[1]. The same document notes that control of cravings at week 104 still favoured semaglutide ^[1].

STEP 4 compared continuing with stopping earlier in treatment. After 20 weeks on semaglutide, people who continued lost a further 7.9% on average by week 68, while those switched to placebo regained 6.9% ^[3].

Tirzepatide (Zepbound®) over time

These trials enrolled different people, for different lengths of time and with different designs from the semaglutide trials above, so the figures describe each medicine in its own studies and are not a comparison between them.

SURMOUNT-1 gave 2,539 adults without diabetes weekly tirzepatide 5, 10 or 15 mg or placebo for 72 weeks. Average changes were −15.0%, −19.5% and −20.9% against −3.1%; 85% to 91% on tirzepatide lost at least 5%, and 50% and 57% on the two higher doses lost at least 20% ^[13].

Participants who also had prediabetes stayed on treatment for 176 weeks. At three years the average changes were −12.3%, −18.7% and −19.7% against −1.3% on placebo, which the authors describe as substantial and sustained weight reduction; most stomach side effects came during the first 20 weeks ^[4]. In SURMOUNT-4, people who had lost 20.9% over a 36-week lead-in and stayed on tirzepatide lost a further 5.5% by week 88, while those switched to placebo regained 14.0% ^[5]. Our article on stopping a GLP-1 covers those withdrawal results in more depth.

Other things that can hold weight steady

• Medicines and health conditions: MedlinePlus keeps a list of medicines and hormone or health problems that can add weight, from corticosteroids to an underactive thyroid; our article on not losing weight on a GLP-1 goes through it item by item ^[10].
• Fluid: build-up of fluid in the tissues, including around menstruation, can add weight that is not fat; MedlinePlus says rapid weight gain can be a sign of dangerous fluid retention ^[10].
• Stopping smoking can lead to weight gain that is not simply due to eating more ^[10].
• Daily life: the NIDDK says a lifestyle programme can address eating triggers and short sleep, two things that push weight up ^[7].
• If you suspect one of your medicines, MedlinePlus says to raise it with your provider rather than stop it yourself ^[10].

What not to change on your own

A plateau can make it tempting to take more, inject more often or climb a step early. The Wegovy® label allows a dose above its usual maintenance options only in adults who have tolerated the usual dose for at least 4 weeks and when further weight reduction is clinically indicated, and the Zepbound® label sets a maximum weekly dose ^[8][9]. Those are prescriber decisions.

The FDA says it has had adverse event reports linked to compounded semaglutide or tirzepatide used above label doses, whether as bigger single doses, more frequent doses or a faster climb; some people needed medical care for stomach symptoms such as nausea, vomiting, diarrhea, pain or constipation ^[11].

Questions worth bringing to your clinician

• How long have I been on my current dose, and is this the dose you intended for maintenance?
• Has anything else changed: sleep, activity, a new medicine, or how much I eat as my appetite returns?
• Could a medicine or a health condition be adding weight, and is anything worth testing?
• The NIDDK describes a review after 12 weeks on the full dose, with less than 5% loss as the usual point to discuss stopping. Where am I against that?
• Apart from weight, which measures are worth watching, such as waist size, blood pressure or blood sugar?

Reading the trend rather than the day

The trials judged weight change over 68 and 72 weeks, not over a week or two ^[12][13]. A flat fortnight means more when it is set against what else happened: a missed dose, a new medicine, a run of short nights or the days around a period, which can add fluid ^[10].

Bringing that record to your appointment lets your clinician see the plateau in context rather than as one number. The decision about what, if anything, to change stays with them.

Wegovy® is a registered trademark of Novo Nordisk A/S. Zepbound® is a registered trademark of Eli Lilly and Company. PepLabo is not affiliated with or endorsed by Novo Nordisk or Eli Lilly and Company.