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 the Evidence Shows
When considering Mounjaro (tirzepatide) for weight management, it's natural to wonder what real results look like. Clinical trials show meaningful weight loss, but "before and after" comparisons vary significantly between individuals. This guide explains the evidence behind Mounjaro weight loss, how it compares to Wegovy, and why individual results differ. Both medications require a prescription and clinical assessment from a UK-licensed prescriber.
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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.
Clinical Trial Data: Mounjaro vs Wegovy Results
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it works on two hormone pathways simultaneously, which may explain stronger average results. The SURMOUNT-1 clinical trial tracked 3,731 adults over 72 weeks:
- 5 mg dose: average weight loss ~15% of body weight
- 10 mg dose: average weight loss ~19.5% of body weight
- 15 mg dose (maximum): average weight loss ~20.9% of body weight
Wegovy (semaglutide) is a single GLP-1 receptor agonist. The STEP-1 clinical trial showed average weight loss of approximately 14.9% of body weight at the maximum 2.4 mg dose over 68 weeks. Both medications were used alongside a reduced-calorie diet and increased physical activity — medication alone does not produce these results. Individual weight loss varies considerably depending on baseline weight, age, genetics, diet adherence, and activity level.
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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.
Why Results Vary: Individual Suitability Matters
There is no "standard" before and after for weight loss injections because every person responds differently. Some individuals lose 15% of their body weight; others lose 10% or 25%. Age, metabolism, baseline weight, adherence to diet and exercise, and individual hormone sensitivity all affect outcomes. Your GP or prescriber will assess which medication—if either—suits your health profile, medical history, and weight management goals. Use our free GLP-1 weight loss calculator above to explore projected weight loss at different doses, remembering that actual results may differ. Both Mounjaro and Wegovy require ongoing medical oversight and are prescribed as part of a comprehensive weight management plan, not as standalone solutions.
- 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.
Are Mounjaro results better than Wegovy results?
Clinical trials show Mounjaro achieved slightly higher average weight loss (up to 20.9%) compared to Wegovy (14.9%), but the difference is modest and individual results vary widely. Neither medication "assures" specific weight loss. Your prescriber will recommend the most appropriate option based on your health profile and medical history. Both are prescription-only and require a clinical assessment.
Can I use "before and after" photos to predict my own results?
No. Before and after comparisons you see online may represent exceptional results or be from people with different starting weights, ages, or lifestyle factors. Clinical trials show average outcomes, but individual results range widely. Use our weight loss calculator as a realistic projection tool, and discuss personal expectations with your prescriber during your initial consultation.
How quickly will I see weight loss results on Mounjaro?
Most people begin noticing appetite reduction within the first few weeks. Measurable weight loss typically becomes apparent after 4–8 weeks, with ongoing results over 12–16 weeks as doses are increased. Weight loss continues as long as you take the medication alongside a reduced-calorie diet and physical activity. Stopping the medication may lead to weight regain over time.
Is Mounjaro or Wegovy better for me personally?
This requires a clinical assessment by your GP or a UK-licensed prescriber. Both are prescription-only and available through NHS specialist services or private prescribing. Your prescriber will consider your medical history, current medications, weight, BMI, and any weight-related health conditions to recommend the most suitable option. Calculate your BMI using our free tool above to understand your starting point.
What if I don't lose as much weight as the clinical trials showed?
Weight loss on any medication depends on adherence to diet and exercise changes, individual metabolism, and other health factors. If results plateau, your prescriber may adjust your dose or explore whether the medication continues to be appropriate. Sustainable weight management typically requires ongoing lifestyle changes alongside any medical treatment.
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.