Results & Expectations

How Much Weight Can You Lose?

Find out how much weight you can lose with Mounjaro or Wegovy, including average results, timelines, and what affects progress.

Whether you are weighing up whether weight-loss injections are worth starting or trying to manage expectations a few months in, this guide answers the most-asked question in the category: how much weight can you actually lose on Mounjaro, Wegovy or retatrutide? It draws on published trial data, real-world considerations, and the genuine variability between individuals. LetsLoseWeight is an independent comparison site; we do not prescribe medication. The figures below are averages from clinical trials — your results will be your own.

The headline trial numbers

Three medicines dominate the conversation. Two are licensed in the UK; one is investigational. Average weight loss in their pivotal trials, after roughly 16–18 months of treatment alongside lifestyle changes:

Medicine Trial Duration Highest licensed dose Average weight loss Placebo group
Mounjaro (tirzepatide) SURMOUNT-1 72 weeks 15mg weekly ~20.9% ~3.1%
Mounjaro (tirzepatide) SURMOUNT-1 72 weeks 10mg weekly ~19.5% ~3.1%
Mounjaro (tirzepatide) SURMOUNT-1 72 weeks 5mg weekly ~15.0% ~3.1%
Wegovy (semaglutide 2.4mg) STEP 1 68 weeks 2.4mg weekly ~14.9% ~2.4%
Retatrutide (investigational) Phase 2 obesity trial 48 weeks 12mg weekly ~24.2% ~2.1%

Sources: Jastreboff et al., NEJM 2022 (SURMOUNT-1), Wilding et al., NEJM 2021 (STEP 1), Jastreboff et al., NEJM 2023 (retatrutide).

The first thing those numbers tell you is that the medicine matters less than people often think. The gap between Wegovy and the highest-dose Mounjaro is real but it is not vast — and individual response varies more than the headline averages suggest.

Translating percentages to kilos and pounds

Percentages are how trials report. Most patients want kilos. Rough translations for a person on the highest licensed dose of Mounjaro (around 21% average loss):

  • Starting weight 90 kg (14 stone 2 lb) — average loss around 19 kg / 42 lb / 3 stone
  • Starting weight 100 kg (15 stone 10 lb) — average loss around 21 kg / 46 lb / 3 stone 4 lb
  • Starting weight 120 kg (18 stone 12 lb) — average loss around 25 kg / 55 lb / 3 stone 13 lb

For Wegovy at 2.4mg (around 15% average loss):

  • Starting weight 90 kg — average loss around 13.5 kg / 30 lb / 2 stone 2 lb
  • Starting weight 100 kg — average loss around 15 kg / 33 lb / 2 stone 5 lb
  • Starting weight 120 kg — average loss around 18 kg / 40 lb / 2 stone 12 lb

These are averages — half of trial participants lost more, half lost less. Some lost very little; some lost more than 30%.

What "average" hides

The average masks important variation. In SURMOUNT-1, on the 15mg dose:

  • About 57% of participants achieved at least 20% weight loss
  • About 36% achieved at least 25% weight loss
  • About 7% lost less than 5% — the threshold often used to define a clinically meaningful response

In STEP 1 on Wegovy 2.4mg:

  • About 50% of participants achieved at least 15% weight loss
  • About 32% achieved at least 20%
  • A small minority lost less than 5%

What this means in practice: if you are starting treatment, the most likely outcome is that you will lose a meaningful amount of weight, but you cannot reliably predict in advance whether you will be at the upper or lower end of the range.

Real-world results vs. trial results

Trial conditions are not real life. Trial participants:

  • Have closely monitored dose titration with structured support
  • Receive lifestyle counselling as part of the protocol
  • Are screened to exclude many medical conditions that could affect outcomes
  • Tend to be more adherent than typical real-world patients

Real-world studies of Mounjaro and Wegovy in everyday clinical practice generally show somewhat smaller average weight losses than trials, though the gap is not huge — typically a few percentage points. The biggest single factor is adherence: people who stay on the medicine and titrate to a maintenance dose see results closer to trial averages.

How dose affects results

Both medicines are dose-dependent — higher doses produce more weight loss on average:

  • Mounjaro: ~15% at 5mg, ~19.5% at 10mg, ~20.9% at 15mg
  • Wegovy: ~10% at lower titration doses, ~15% at the full 2.4mg maintenance dose

The differences between dose levels are real, but they are also incremental — each step up gives a few percentage points more on average, with the rate of additional benefit slowing at the highest doses. For some patients, the side-effect cost of the highest dose outweighs the small additional weight loss benefit; settling on a tolerable maintenance dose is often the right answer even if it is not the maximum.

For the licensed dose schedules, see the Mounjaro dosing guide and Wegovy dosing guide.

How long results take

Most patients see:

  • Reduced appetite within 1–2 weeks of starting
  • Steady weight loss starting in the first month as the dose builds up
  • Most weight loss occurring in the first 6–9 months, with a slower phase after that
  • Plateau around 12–18 months at maximum trial-reported weight loss

For a more detailed timeline, see our when do you see results guide.

What happens if you stop

Weight regain after stopping is common. The STEP 1 trial extension followed participants for a year after stopping semaglutide and found that, on average, two-thirds of the lost weight was regained within 12 months (Wilding et al., 2022).

Comparable long-term withdrawal data for tirzepatide is more limited but follows a similar pattern in published trials. Retatrutide's withdrawal phase has not been published.

This is one of the most important points for thinking about whether to start. Weight-loss injections are not a short course of treatment. The medicine is licensed as an adjunct to lifestyle change, and the evidence suggests that lifestyle change is what holds the weight loss when the medicine eventually stops.

Factors that affect individual results

Beyond medicine and dose, the biggest drivers of individual variation are:

  • Adherence — staying on the medicine, titrating to a maintenance dose, taking it weekly without long gaps
  • Lifestyle changes — calorie deficit, dietary quality, physical activity, sleep, stress
  • Starting weight and metabolism — heavier patients lose more in absolute terms; metabolic differences influence responsiveness
  • Genetics — some people respond more to GLP-1-class medicines than others
  • Other medical conditions — type 2 diabetes, thyroid disease, mental health conditions can all influence outcomes
  • Other medications — some can blunt or amplify weight effects

For a fuller breakdown, see our what affects results guide.

What "good" results look like

NICE guidance and most clinical guidelines define a clinically meaningful response as at least 5% weight loss. The average response on Mounjaro or Wegovy is well above that threshold, but the threshold matters because it is the level at which weight-related health markers (blood pressure, lipids, glucose, liver fat, sleep apnoea) typically improve.

Setting realistic expectations is more useful than chasing the maximum. Most published guidance suggests aiming for 5–15% weight loss in the first year — comfortably within the trial-average range — and reviewing whether to continue, change dose, or change medicine if you fall significantly short.

Frequently asked questions

Will I lose 20% on Mounjaro?
On average, on the 15mg dose, yes — but "average" hides a wide range. About 57% of trial participants on 15mg lost at least 20%; some lost more, some lost less. There is no way to predict in advance which group you will be in.

Why do some people lose much more than the average?
Genetics, adherence, dietary changes, exercise, sleep, and individual responsiveness to GLP-1 medicines all play a role. Some patients on these medicines lose 30% or more — this is the upper end of the trial range, not a typical outcome.

Why do some people lose almost nothing?
A small minority of patients are "non-responders" — they either tolerate the medicine but don't lose weight, or they cannot tolerate the dose increases needed to reach a clinically effective level. If you are not seeing at least 5% loss after 6 months at a maintenance dose, talk to your prescriber about whether to continue, switch medicine, or stop.

How does this compare with bariatric surgery?
Bariatric surgery typically produces 25–35% weight loss on average and tends to be more durable. Weight-loss injections produce 15–20% on average and require ongoing treatment. The two are not direct substitutes; some patients move between them.

Will I keep losing weight forever?
No. Weight loss typically slows after 6–9 months and plateaus by 12–18 months. After that, the medicine helps maintain the new lower weight — but does not continue to drive ongoing loss in most patients.

Can I lose weight without lifestyle changes?
The trials all included lifestyle interventions, so the average results assume some lifestyle change. Patients who do not change their diet or activity at all tend to lose less. The medicine is licensed as an adjunct to lifestyle changes, not a replacement for them.

Next steps

Sources

This guide is for general information only and is not a substitute for professional medical advice. Average trial figures do not predict individual results.

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How Much Weight Can You Lose on Weight Loss Injections | LetsLoseWeight