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 vs Wegovy: UK Success Stories and Real Results
Both Mounjaro and Wegovy are prescription-only weight loss injections approved in the UK, but they work differently and achieve different average results. Success with either medication depends on your individual health, how your body responds, and whether you combine treatment with lifestyle changes. This guide compares clinical trial data from both medicines to help you understand what realistic outcomes look like.
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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 Results: SURMOUNT vs STEP Data
Mounjaro (tirzepatide) and Wegovy (semaglutide) have both been rigorously tested in UK-approved clinical trials, giving us clear data on average weight loss outcomes.
Mounjaro (SURMOUNT-1 trial): Participants taking the maximum 15 mg dose lost an average of approximately 20.9% of their body weight over 72 weeks alongside a reduced-calorie diet and increased physical activity. At the 10 mg dose, average loss was around 19.5%.
Wegovy (STEP-1 trial): Participants on the 2.4 mg maximum dose achieved an average weight loss of approximately 14.9% of body weight over 68 weeks, also with diet and exercise support.
It's crucial to understand these are average results — individual outcomes vary significantly. Some people lose more, some less. Our GLP-1 weight loss calculator can help you explore projected results at different dose levels. Success isn't assured; it's achieved through consistent use alongside lifestyle changes.
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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 Differ: Mechanism and Individual Factors
The key difference between these medications explains some variation in results. Mounjaro is a dual GIP and GLP-1 receptor agonist — it activates two natural hormone pathways simultaneously, which may contribute to greater appetite suppression and weight loss for some people. Wegovy is a GLP-1 only agonist, activating a single pathway.
However, "better average results" doesn't mean Mounjaro is right for everyone. Success depends on how your body responds, your adherence to the medication schedule, whether you're taking a UK prescription weight loss injection with consistent lifestyle changes, your baseline health, and genetics. Your prescriber will assess which medication suits you individually during your clinical assessment. Use our free BMI calculator and weight converter to track your current health metrics as a baseline.
Real success in the UK with either medication means more than the number on the scale. It includes improved blood pressure, better blood sugar control, reduced joint pain, improved sleep, and increased energy levels — benefits that often appear before major weight loss. Many people also experience positive changes in how their clothes fit or how they feel physically before reaching their target weight. Progress tracking is essential; use our free progress tracker to log these non-scale victories alongside weight measurements, which often matter more for long-term health.
- 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 switch from Wegovy to Mounjaro if I'm not seeing results?
Yes, prescriber-managed switches are possible. There's no official conversion chart, but approximate equivalence exists (e.g. Wegovy 1.7 mg ≈ Mounjaro 10 mg). Any switch must be managed by your prescriber — never stop one and start another without medical guidance. You may need a washout period between medications.
What percentage of people lose significant weight on Mounjaro vs Wegovy in real UK practice?
Clinical trials showed approximately 85% of Mounjaro users and 80% of Wegovy users experienced meaningful weight loss. However, real-world UK outcomes may differ from trial conditions. Adherence, diet, and exercise consistency matter as much as the medication itself.
How long does it take to see weight loss success on these injections?
Most people notice appetite changes within 1–2 weeks. Measurable weight loss typically becomes apparent after 4–8 weeks. Maximum results usually require 16–20 weeks of consistent use. Patience is essential; rapid results are unusual.
Are there NHS success stories with Mounjaro or Wegovy available?
Limited published UK NHS patient outcomes exist publicly. Most documented success stories come from clinical trials and private prescribing. Your GP or specialist can discuss realistic expectations based on your individual profile during assessment.
Do I need to continue other medications alongside Mounjaro or Wegovy?
This depends entirely on your health profile. If you take diabetes, blood pressure, or cholesterol medications, your prescriber may adjust doses as you lose weight. Never stop any medication without medical guidance — weight loss medication works alongside, not instead of, other treatments.
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.