# How much weight will you lose on a GLP-1? What the trials — and real life — show

> How much weight do people lose on Ozempic/Wegovy (semaglutide) and Mounjaro/Zepbound (tirzepatide)? In the big trials, averages ran about 15–21% of body weight — but those are group means, real-world results are lower (~9% at a year), and most of it comes back if you stop. Here's the honest picture.

**Evidence grade:** Established (rung 1 of 8 on the Peptide Evidence Ladder) · **Last reviewed:** 2026-07-20 · **Source page:** https://thepeptideera.com/evidence/glp1-expected-weight-loss

## Short answer
In the large trials, weight-management doses of these medicines produced big average losses: semaglutide 2.4 mg (Wegovy) averaged about 15% of body weight over 68 weeks, and tirzepatide (Zepbound) averaged roughly 15–21% depending on dose over 72 weeks — versus 2–3% on placebo. But those are group averages, and individual results vary enormously: in the semaglutide trial about half of people lost 15% or more while roughly one in seven didn't reach even 5%. Real-world results are typically lower than the trials — around 9% at one year in a large clinical cohort — mostly because many people stop early or never reach the full dose. And weight tends to return after stopping. So the honest answer isn't a number you can count on; it's a range, driven by dose, how long you stay on, and your own biology. This page reports what the studies found and is not a prediction of your result or medical advice.

## Key takeaways
- Trial averages were large — but they're averages. In STEP 1, adults on semaglutide 2.4 mg (Wegovy) lost about 15% of body weight on average over 68 weeks (vs ~2.4% on placebo). In SURMOUNT-1, tirzepatide (Zepbound) averaged roughly 15% at the low dose up to ~21% at the top dose over 72 weeks (vs ~3% placebo). These are group means, not a personal forecast.
- Individual results vary enormously. In the semaglutide trial, about half of people lost ≥15% and roughly a third lost ≥20% — but around 1 in 7 didn't reach even 5% ("non-responders"). Real people land anywhere from more than 25% to almost nothing.
- Real-world loss is lower than the trials. In a large clinical cohort (~7,900 adults), average loss at one year was about 9% — well below the trial means — mostly because many people stopped early or stayed on low doses. Those who stayed on lost ~12%; those who stopped early lost ~4%.
- How much you lose depends on reaching and staying on the maintenance dose. The headline numbers come from people who completed the full escalation and kept going. Lower doses and stopping early both mean less weight lost.
- It largely comes back if you stop. A year after stopping semaglutide, trial participants regained about two-thirds of the weight they'd lost. These medicines treat weight while you take them; they aren't a one-time reset. What's right for you — including whether to start at all — is a clinician's conversation, not a number off a chart.

## Safety essentials worth knowing

These apply to GLP-1 and dual/triple-agonist medicines generally. They’re label-level points, not the full list, and not advice about you — your prescriber and the FDA label are the authority.

- **Pregnancy & breastfeeding:** these medicines are not recommended in pregnancy, and intentional weight loss is generally not advised in pregnancy; the labels advise stopping before a planned pregnancy. Breastfeeding status is a conversation to have with your clinician.
- **Birth control:** some of these medicines (such as tirzepatide) can make *oral* contraception less reliable. If you could become pregnant, ask about backup or non-oral contraception.
- **Thyroid boxed warning:** this drug class carries an FDA boxed warning (thyroid C-cell tumours seen in rodents) and is not for people with a personal or family history of medullary thyroid cancer (MTC) or MEN 2.
- **Blood sugar:** combined with insulin or a sulfonylurea, these medicines can cause low blood sugar — those other medicines often need prescriber-managed adjustment, not self-adjustment.
- **Eating disorders:** an appetite-suppressing medicine warrants particular caution with a current or past eating disorder; disclose this to your clinician.
- **Surgery, sedation & endoscopy:** because these medicines slow stomach emptying, tell your surgical or anaesthesia team you take a GLP-1 well in advance — they'll decide with you whether to continue or hold it (more: https://thepeptideera.com/evidence/glp1-and-surgery).

"How much weight will I lose?" is the first question almost everyone asks — and the honest answer is a range, not a number. The trials behind these prescription medicines produced some of the largest average weight losses recorded for a weight-management drug. But an average is a fact about a *group*, not a promise to *you*, and the gap between the trial headline and a real person's year can be wide. Here's the whole picture, including the parts the ads leave out.

## What the big trials actually found

Two landmark trials set the expectations, both in adults with obesity or overweight and *without* diabetes, both against placebo plus lifestyle support.

- **Semaglutide 2.4 mg (Wegovy) — STEP 1**, 1,961 adults over 68 weeks: mean weight change **−14.9%**, versus −2.4% on placebo. About **15% of body weight, on average.**
- **Tirzepatide (Zepbound) — SURMOUNT-1**, 2,539 adults over 72 weeks: mean change of about **−15.0% at 5 mg, −19.5% at 10 mg, and −20.9% at 15 mg**, versus −3.1% on placebo. (You'll often see "up to 22.5%" quoted — that's a different, more optimistic statistical estimand that assumes full adherence. The numbers here are the more conservative, more honest ones.)

Those are real, and they're why these drugs changed the field. But read them as **what the average participant achieved**, not as your target.

## The averages hide enormous variation

The single most misleading thing about a mean is that almost no one *is* the mean. In STEP 1, the spread was huge:

| Weight lost | Share of people on semaglutide |
|---|---|
| ≥ 5% | ~86% |
| ≥ 10% | ~69% |
| ≥ 15% | ~51% |
| ≥ 20% | ~32% |

So about half reached 15% or more, and roughly a third reached 20% — genuinely striking. But look at the other end: around **one in seven didn't even reach 5%.** These are the [non-responders](/articles/glp1-non-responders/), and they were in the trial too. Real results run from more than 25% loss to almost nothing, and there is currently **no reliable way to predict in advance** which end you'll land on.

## Why real life comes in lower than the trials

Trial numbers describe near-ideal conditions: free medication, structured support, and people who completed a full dose escalation. Outside a trial, the average is lower. In a large clinical cohort of roughly 7,900 adults, mean weight loss at one year was about **9%** — meaningfully below the ~15% trial figure. The reason isn't that the drug stopped working; it's mostly **dose and duration**:

- People who **stayed on** the medicine lost about **12%**;
- those who discontinued later lost about **7%**;
- those who **stopped early** lost about **4%**.

Most were also on lower maintenance doses than the trial's top dose. The lesson isn't "the trials lied" — it's that the headline number belongs to people who reached the full dose and kept going, and that reaching it is where much of real life diverges.

## It largely comes back if you stop

Weight loss on these drugs is a treatment effect, not a cure. In the STEP 1 extension, participants **regained about two-thirds** of the weight they had lost within a year of stopping. In STEP 4, people who switched to placebo at week 20 began regaining, while those who continued kept losing. This is one of the most important and least-advertised facts about the whole class, and it's why the decision to start is really a decision about a [longer-term plan](/evidence/stopping-glp1), made with a clinician — not a short course.

## Which one takes off more weight?

Head-to-head, tirzepatide edged out semaglutide: in **SURMOUNT-5**, a 72-week trial comparing them directly, tirzepatide averaged **−20.2%** versus semaglutide's **−13.7%**. So on the current evidence tirzepatide (Mounjaro/Zepbound) produces somewhat more weight loss on average than semaglutide (Ozempic/Wegovy) — though both are highly effective, tolerability and access differ, and "more on average" still isn't a promise for any one person. We compare them in more depth on the [semaglutide vs tirzepatide](/evidence/semaglutide-vs-tirzepatide/) page.

> A note on brands: the biggest weight-loss numbers come from the **weight-management** doses — Wegovy (semaglutide 2.4 mg) and Zepbound (tirzepatide). The diabetes versions at their usual doses — Ozempic, Mounjaro — tend to produce somewhat less, because the dose and the studied population differ.

## What this means if it's you

The useful version of "how much will I lose" isn't a percentage — it's a set of levers and a range. On today's evidence, GLP-1 and GIP/GLP-1 medicines produce **clinically significant weight loss** for most people who take them at an effective dose (that part is well established). But *your* specific result isn't predictable, real-world averages run below the trial headlines, and the weight tends to return if you stop.

It also helps to remember what the number is *for*. Clinically, weight loss is a means to health — better blood sugar, blood pressure, and cardiometabolic risk, and relief for things like sleep apnea and joints — not a score in itself. Even a loss in the **5–10%** range delivers meaningful metabolic benefit, so landing below the trial average is often still a real success, not a failure. Two things shape whether the loss you get is *good* weight loss: staying at an effective dose, and protecting muscle with enough protein and some resistance training, since a share of any weight lost is lean mass.

And these are **prescription** medicines with real indications: the trials studied adults with obesity or overweight who met specific criteria, and they are not intended for cosmetic weight loss in people without a medical indication. Some people shouldn't take them at all or need extra care — in pregnancy, with a personal or family history of medullary thyroid cancer or MEN 2, or with a history of pancreatitis (see the [side-effects](/evidence/glp1-side-effects/) rundown). Whether to start, which medicine, and what a realistic goal looks like is a conversation with a clinician who can weigh your history — not a figure to lift from a study. You can use our [progress tool](/tools/trajectory-check) to understand the normal range of results, real-world included, rather than to grade yourself against a trial curve.

## Frequently asked questions

**How much weight will I lose on Ozempic or Wegovy?**
In the STEP 1 trial, adults on the weight-management dose of semaglutide (Wegovy 2.4 mg) lost **about 15% of body weight on average** over 68 weeks — but that's a group mean. About half lost 15% or more, while roughly one in seven lost less than 5%. Real-world averages are lower (around 9% at a year), largely because many people stop early or don't reach the full dose. Ozempic (the diabetes brand of semaglutide) is usually dosed lower and tends to produce somewhat less. None of this predicts your individual result.

**How much weight will I lose on Mounjaro or Zepbound?**
In SURMOUNT-1, tirzepatide (Zepbound) averaged roughly **15% at 5 mg up to about 21% at 15 mg** over 72 weeks — versus about 3% on placebo. As with semaglutide, individual results vary widely and real-world loss tends to run lower than the trial. The diabetes brand (Mounjaro) at typical doses generally produces somewhat less than the weight-management dosing.

**Why am I losing less weight than the trials say?**
Very common, and usually not a sign anything is wrong. Trial averages reflect people who reached the full maintenance dose and stayed on it with structured support; real-world loss averages lower (~9% at a year). Dose, how long you've been on it, and your own biology all matter. If your loss has stalled, our page on the [weight-loss plateau](/evidence/glp1-plateau/) explains why — and it's worth raising with your prescriber rather than self-adjusting.

**Will I keep the weight off if I stop?**
Mostly not, on current evidence: about **two-thirds** of lost weight was regained within a year of stopping semaglutide in the STEP 1 extension. These medicines work while you take them. Whether, when, and how to stop is a clinical decision — see [what happens when you stop](/evidence/stopping-glp1/).

**Which causes more weight loss, Ozempic or Mounjaro?**
In a direct head-to-head trial (SURMOUNT-5), tirzepatide averaged more weight loss than semaglutide (−20.2% vs −13.7%). So tirzepatide (Mounjaro/Zepbound) tends to produce more on average — but both are highly effective, and the right choice depends on tolerability, cost, access and your history, not the average alone.

## Sources (6)
1. Wilding JPH, et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1). N Engl J Med. 2021;384:989–1002. (1,961 adults, 68 weeks; mean −14.9% vs −2.4% placebo; ≥5% 86.4%, ≥10% 69.1%, ≥15% 50.5%, ≥20% ~32%.) — https://www.nejm.org/doi/full/10.1056/NEJMoa2032183 [RCT]
2. Jastreboff AM, et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). N Engl J Med. 2022;387:205–216. (2,539 adults, 72 weeks; treatment-regimen estimand −15.0% (5 mg), −19.5% (10 mg), −20.9% (15 mg) vs −3.1% placebo. The often-quoted 'up to 22.5%' is the efficacy/on-treatment estimand.) — https://pubmed.ncbi.nlm.nih.gov/35658024/ [RCT]
3. Aronne LJ, et al. Tirzepatide as Compared with Semaglutide for the Treatment of Obesity (SURMOUNT-5). N Engl J Med. 2025;393(1):26–36. (Head-to-head, 72 weeks; tirzepatide −20.2% vs semaglutide −13.7%, P<0.001.) — https://pubmed.ncbi.nlm.nih.gov/40353578/ [RCT]
4. Wilding JPH, et al. Weight regain and cardiometabolic effects after withdrawal of semaglutide: the STEP 1 trial extension. Diabetes Obes Metab. 2022;24:1553–1564. (Completers regained about two-thirds of lost weight within a year of stopping.) — https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9542252/ [RCT]
5. Rubino D, et al. Effect of Continued Semaglutide vs Placebo on Weight Loss Maintenance (STEP 4, randomized withdrawal at week 20). JAMA. 2021;325:1414–1425. (Switching to placebo led to regain; continuing led to further loss.) — https://pubmed.ncbi.nlm.nih.gov/33755728/ [RCT]
6. Gasoyan H, et al. Real-world weight loss with semaglutide/tirzepatide (Cleveland Clinic EHR cohort, ~7,900 adults without diabetes): mean ~8.7% at 1 year; by adherence 3.6% (early discontinuers) / 6.8% / 11.9% (stayed on). — https://www.ajmc.com/view/real-world-use-of-glp-1s-yields-less-weight-loss-than-clinical-trials [OBSERVATIONAL]

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From The Peptide Era (https://thepeptideera.com) — evidence-graded, primary-sourced answers about GLP-1 medicines. Education, not medical advice. No doses, no sourcing.