Mounjaro (tirzepatide) has produced some of the most significant weight loss results seen in clinical trials. This guide covers the SURMOUNT trial data and a realistic week-by-week progression for UK patients.
Estimated progress calculator
Illustrative estimate interpolated from SURMOUNT-1 trial averages for patients following the standard dose escalation to 15mg. Individual results vary considerably — this is not a prediction for any one person.
Clinical Trial Results: The SURMOUNT Trials
- Mounjaro 5mg: approximately 15% of body weight over 72 weeks
- Mounjaro 10mg: approximately 19.5% of body weight over 72 weeks
- Mounjaro 15mg: approximately 22.5% of body weight over 72 weeks
For someone starting at 100kg, Mounjaro 15mg delivered an average loss of 22.5kg over 72 weeks (about 17 months) — significantly greater than any previous weight loss medication.
Week-by-Week Timeline
Weeks 1–4 (2.5mg)
Appetite reduction usually begins within the first week. Weight loss is modest — typically 0.5–1.5kg. Side effects, particularly nausea, are most common now. The goal here is tolerability, not maximum loss.
Weeks 5–8 (5mg)
Appetite suppression becomes more noticeable. Weight loss accelerates to 1–2kg per month. Total loss by week 8: often 3–6kg.
Weeks 9–16 (7.5mg and 10mg)
Often the most noticeable physical changes. Monthly loss: 2–3kg is typical. By week 16, many patients have lost 8–12kg.
Weeks 17–36 (12.5mg and 15mg)
Maximum weight loss rate is typically reached at these doses. By week 36, SURMOUNT data shows average losses of 18–20% of starting body weight at 15mg.
Week 72 and Beyond
By the end of the 72-week SURMOUNT-1 trial: average total loss 22.5% of body weight at 15mg, with 57% of participants losing 20% or more.
What Happens When You Stop?
Weight typically returns, sometimes rapidly, once Mounjaro is stopped — the SURMOUNT-4 trial found most patients regained a significant proportion of lost weight within 52 weeks of stopping. This doesn't mean Mounjaro doesn't work; it means it works while you take it, similar to blood pressure medication. Many UK prescribers now discuss maintenance prescribing as part of the treatment plan.
Factors That Influence Your Results
- Starting weight and BMI
- Diet — works best alongside a calorie-controlled diet
- Physical activity — preserves muscle mass and improves outcomes
- Dose reached — 15mg produces more loss than lower doses
- Consistency — skipping injections reduces effectiveness
- Underlying conditions — thyroid disorders, PCOS, and certain medications can slow progress
See our dose schedule guide and price comparison for next steps.
Frequently Asked Questions
How much weight will I lose on Mounjaro?
Clinical trial averages are 22.5% of body weight on the maximum 15mg dose over 72 weeks. Individual results vary; most people see meaningful loss (5–10%) within the first three months.
How quickly does Mounjaro start working?
Appetite reduction typically begins within the first week. Measurable weight loss usually appears within 2–4 weeks.
Will I regain weight when I stop?
Yes — clinical data shows most people regain a significant amount after stopping. Discuss a maintenance plan with your prescriber.