The UK's most complete GLP-1 guide
Every Question Answered. Every Side Effect Explained.
- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
- What to eat on treatment
- FAQs answered
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Mounjaro Before and After — What Clinical Evidence Shows
Many people considering Mounjaro (tirzepatide) wonder what realistic before and after results actually look like. The truth is that individual results vary significantly, but clinical trials provide clear evidence of what tirzepatide can help achieve when used alongside a reduced-calorie diet and increased physical activity. This guide explains the research behind Mounjaro weight loss, typical timelines, and what factors influence individual outcomes — so you can understand what to realistically expect from this prescription GLP-1 receptor agonist medication.
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Calculate Your BMI Instantly
Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
What Is BMI and Why Does It Matter?
Body Mass Index (BMI) is the most widely used screening tool for assessing whether your weight falls within a healthy range. Used by the NHS, GPs, and weight management services across the UK, BMI provides a quick snapshot of your weight relative to your height. The formula is simple: your weight in kilograms divided by your height in metres squared (kg/m²).
While BMI isn't a perfect measure — it doesn't account for muscle mass, bone density, or fat distribution — it remains the standard first step in identifying potential weight-related health risks including type 2 diabetes, cardiovascular disease, high blood pressure, and certain cancers.
The NHS also recommends adjusted thresholds for people of South Asian, Chinese, or Black African heritage — a BMI of 23 or above is classified as overweight, and 27.5 as obese. Our calculator includes this adjustment as a one-click toggle.
What Do Clinical Trials Show About Mounjaro Results?
The main evidence for Mounjaro comes from the SURMOUNT clinical trial programme, which tested tirzepatide on thousands of adults with overweight or obesity. In SURMOUNT-1, the largest trial, participants using Mounjaro alongside lifestyle changes achieved significant average weight loss over 72 weeks:
- 5 mg dose: approximately clinically studied weight loss
- 10 mg dose: approximately clinically studied weight loss
- 15 mg dose (maximum): approximately clinically studied weight loss
For perspective, a person weighing 100 kg starting Mounjaro at 15 mg might expect to lose around 20.9 kg (approximately 3 stone 4 lbs) on average — though actual results range widely. The trial participants also followed a reduced-calorie diet (around 500 kcal deficit daily) and increased physical activity, which are essential components of treatment success. These were not weight loss results from the injection alone, but from the complete treatment approach.
Clinically BackedWeight Loss
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How It Works
Three simple steps to understand your weight and take action.
Enter your height and weight in our free calculator. Get your BMI, NHS category, healthy weight range, and ethnicity-adjusted thresholds instantly.
If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
When Do You See Results, and What Influences Your Personal Outcome?
Most people start Mounjaro at 2.5 mg and gradually increase to a maintenance dose over 16–20 weeks. Weight loss typically becomes noticeable between weeks 4 and 8, though some people see changes earlier or later. The first dose increase (to 5 mg) often triggers more noticeable appetite suppression and weight loss acceleration. However, your personal before-and-after results depend on several factors: your starting weight, how well you maintain the reduced-calorie diet, your physical activity level, your metabolism, and genetic factors. Some people lose steadily; others experience plateaus. This is completely normal. Your GP or prescriber can discuss what realistic targets might look like for your specific situation, and our free weight loss calculator can help you estimate potential results at different doses.
- Dual GIP/GLP-1 receptor agonist
- Up to 22.5% body weight loss (SURMOUNT-1)
- Weekly injection, dose escalation over 20+ weeks
- Available via private prescription in the UK
- Doses: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg
- GLP-1 receptor agonist
- Up to 15–17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg
Mounjaro vs Wegovy: Head-to-Head
A side-by-side comparison of the two most popular GLP-1 weight loss medications available in the UK.
| Feature | Mounjaro | Wegovy |
|---|---|---|
| Drug class | Dual GIP/GLP-1 agonist | GLP-1 agonist |
| Active ingredient | Tirzepatide | Semaglutide |
| Avg. weight loss | 15–22.5% | 12–17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20–32 weeks | 16–20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | £150–£250/month | £150–£300/month |
| Common side effects | Nausea, diarrhoea, constipation | Nausea, vomiting, diarrhoea |
Data sourced from SURMOUNT-1 and STEP 1 clinical trials. Costs are approximate and vary by provider. Always consult a prescriber.
Am I Eligible for Weight Loss Medication?
In the UK, eligibility for GLP-1 weight loss medications like Mounjaro and Wegovy is based on your BMI and overall health profile.
- BMI of 30 or above (obese)
- Age 18 or over
- No contraindicated conditions
- Committed to lifestyle changes
- BMI of 27 or above
- Plus type 2 diabetes
- Or high blood pressure
- Or obstructive sleep apnoea
Use our BMI calculator to check whether your BMI falls within the eligible range.
How We Built These Tools
Every calculator and guide on myweightcheck is built with accuracy and transparency in mind. Our BMI calculator uses the standard WHO formula with NHS-aligned category thresholds. Our GLP-1 projections are modelled on published clinical trial data from SURMOUNT and STEP studies.
All data stays on your device. We don't require sign-ups, and we don't store your health information on any server. Your progress tracker saves data locally in your browser using localStorage, so only you can see it.
We're based in the UK and our tools are designed specifically for UK users — supporting stone & lbs by default, referencing NHS guidelines, using NICE-approved medication data, and linking to GPhC-registered pharmacies.
Frequently Asked Questions
Common questions about BMI, weight loss medications, and our free UK tools.
Can I see clinically studied weight loss with Mounjaro?
No. While SURMOUNT trials showed average weight loss of 15–21%, individual results vary significantly. Some people lose more, some less. Weight loss depends on adherence to diet, physical activity, and individual metabolism. Mounjaro is a tool to support weight loss alongside lifestyle changes — not a assures. Always discuss realistic expectations with your prescriber.
Why do before-and-after results vary so much between people?
Multiple factors influence results: starting weight, age, metabolism, how strictly you follow a reduced-calorie diet, physical activity level, genetics, other medications, and baseline health conditions. Two people on the same dose can lose different amounts. This is completely normal and expected in weight loss treatment.
How long does it take to see visible Mounjaro results?
Most people notice appetite reduction and early weight loss between weeks 4 and 8. More visible results typically appear after 12–16 weeks as the dose increases and lifestyle changes take effect. Full results from SURMOUNT trials were measured at 72 weeks. Patience is important — sustainable weight loss takes time.
Is Mounjaro a GLP-1 receptor agonist or something different?
Mounjaro (tirzepatide) is unique — it's a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways rather than one. This dual mechanism may explain why some people achieve greater average weight loss with tirzepatide compared to single GLP-1 agonists like semaglutide (Wegovy). However, clinical results still vary individually.
What happens to weight loss when you stop Mounjaro?
Research shows that weight is typically regained after stopping weight loss medication if lifestyle changes are not maintained. This is why Mounjaro is considered a longer-term treatment. The goal is to use the medication to establish new eating habits and physical activity patterns that can be sustained long-term, ideally with support from your GP.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.