Results & Expectations

Results & Expectations

Learn what results to expect from weight loss injections, including how much weight you can lose, timelines, and what affects progress.

Whether you are weighing up Mounjaro, Wegovy or following retatrutide's progress towards possible approval, this is the results and expectations hub for weight-loss injections in the UK. Each section below summarises a part of the picture and links to a deeper guide. The goal: realistic expectations, grounded in published trial data and real-world experience. LetsLoseWeight is an independent comparison site; we do not prescribe medication.

How much weight can you lose?

Trial averages give the headline numbers:

  • Mounjaro 15mg: ~21% average weight loss at 72 weeks (SURMOUNT-1)
  • Mounjaro 10mg: ~19.5% average weight loss at 72 weeks
  • Mounjaro 5mg: ~15% average weight loss at 72 weeks
  • Wegovy 2.4mg: ~14.9% average weight loss at 68 weeks (STEP 1)
  • Retatrutide 12mg: ~24% average weight loss at 48 weeks (phase 2 only — not licensed in UK)

Real-world results tend to run 70–85% of trial averages. Individual variation is wide.

For a fuller breakdown including the spread of outcomes and what predicts above- or below-average results, see our how much weight can you lose guide.

When will you see results?

A typical experience:

  • Weeks 1–2: appetite reduction first noticeable
  • Weeks 3–6: first measurable scale loss
  • Weeks 6–10: clothes start fitting differently
  • Months 4–9: the steepest weight-loss curve
  • Months 12–18: weight stabilises at a new lower set point

For the week-by-week experience, see our when do you see results guide. For the dose-by-dose clinical milestones, see our weight loss timeline guide.

Per-medication results

Each medication has its own pivotal trial:

  • Mounjaro (tirzepatide) — SURMOUNT-1 trial, dose-by-dose averages, real-world context. See our Mounjaro results guide.
  • Wegovy (semaglutide) — STEP 1 trial, the spread of outcomes, cardiovascular benefits via SELECT. See our Wegovy results guide.
  • Retatrutide — phase 2 trial only, not licensed in the UK, important caveats. See our retatrutide results guide.

What affects individual results

Trial averages compress a wide spread. The factors that shift individual results above or below average include:

  • Dose tolerated — higher doses produce greater average weight loss
  • Adherence to the weekly injection schedule
  • Calorie intake and protein — the medicines reduce appetite but do not override active overconsumption
  • Activity, sleep, alcohol, stress
  • Other medications that promote weight gain
  • Underlying conditions like thyroid disease or sleep apnoea
  • Individual biology — genetic and metabolic factors not yet fully characterised

For a deeper dive, see our what affects results guide.

Mounjaro vs Wegovy — the head-to-head

The 2025 SURMOUNT-5 trial was the first head-to-head comparison. Average weight loss was greater with tirzepatide than with semaglutide, with both producing clinically meaningful weight loss (Aronne et al., NEJM 2025).

Individual response varies — some patients lose more on semaglutide than on tirzepatide. The right medicine depends on tolerability, eligibility, cost and prescriber assessment, not just averages. See our Mounjaro vs Wegovy UK comparison.

When results stall — plateau guide

Weight loss in waves rather than smooth lines is normal. Plateaus of 2–4 weeks are routine and usually resolve on their own. Persistent stalls (more than 4–6 weeks at a stable dose with no movement) are worth a conversation with your prescriber.

For practical strategies, see our plateau and not losing weight guide.

What happens when you stop

Average weight regain after stopping is substantial — around two-thirds of lost weight regained within 12 months in the STEP 1 trial extension. This is consistent with the broader picture of obesity as a chronic condition rather than a time-limited problem to fix.

For more, see our what happens when you stop guide.

Beyond weight — what else changes

The medicines have broader cardiometabolic effects on a similar timeline to weight loss:

  • Blood pressure improvements typically begin in the first 12 weeks
  • HbA1c in those with type 2 diabetes — meaningful reductions by 8–12 weeks
  • Lipid panel improvements by 6 months
  • Sleep apnoea severity improves alongside weight loss
  • Joint pain and physical function improve gradually over 6–18 months
  • Cardiovascular events — Wegovy reduced major cardiovascular events by 20% in adults with established cardiovascular disease and overweight/obesity (Lincoff et al., NEJM 2023)

These are part of why the medicines are increasingly considered metabolic medicines rather than just weight-loss drugs.

Setting realistic expectations

A reasonable, evidence-based set of expectations going into treatment:

  • Most patients lose a clinically meaningful amount — typically 10–20% of starting weight on optimal dose, over 12–18 months
  • A meaningful minority lose less than 5% (non-responders) — your prescriber should review at 12 weeks on the maintenance dose
  • Some patients lose more than the headline averages
  • Real-world results tend to be a bit lower than trial results
  • Treatment is long-term — stopping usually means regaining

The expectation worth resisting: dramatic transformation on a fixed timeline. The medicines are powerful, but they work alongside slow lifestyle change, not in spite of slow lifestyle change.

Frequently asked questions

Will I definitely lose weight?
Most patients do, but not all. Around 9–14% of trial participants did not lose meaningful weight even at the highest doses. The first 12 weeks at the maintenance dose is the standard benchmark for assessing personal response.

How fast is "fast enough"?
A common clinical benchmark is at least 5% weight loss by 12 weeks at the maintenance dose. Slower than that warrants review but does not necessarily mean treatment is failing.

Should I expect to look the same as before-and-after photos online?
No — and you probably wouldn't want to. The most striking before-and-after results often involve the highest-responding patients on the highest dose alongside intensive lifestyle work, and rapid weight loss is not always good for body composition or long-term maintenance. Steadier progress at a sustainable rate tends to produce better outcomes.

Does the medicine stop working over time?
Not exactly. The body adapts to lower calorie intake by reducing energy expenditure, which slows the rate of loss. The medicine continues to suppress appetite. Most patients reach a stable lower weight rather than continuing to lose indefinitely.

Next steps

Use the links above to dive into any specific area, or:

Sources

This guide is for general information only and is not a substitute for professional medical advice. Individual results vary. Talk to a qualified prescriber about realistic expectations for your situation.

Get weekly weight loss tips

Join our newsletter for provider updates, expert guidance, and exclusive offers — no spam.

Subscribe free
Back to Guides
Weight Loss Injection Results & Expectations UK Hub | LetsLoseWeight