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 Bundles vs Wegovy in the UK
Mounjaro and Wegovy are both prescription-only weight management injections available in the UK, but they work differently and come in different bundle structures. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, whilst Wegovy (semaglutide) activates GLP-1 only. Both require a clinical assessment before prescription and are used alongside lifestyle changes. This guide compares both medications factually to help you understand the differences — your prescriber will assess which is suitable for your individual health needs.
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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 and Weight Loss Results
Mounjaro (SURMOUNT trials): Participants taking the maximum 15 mg dose lost an average of approximately 20.9% of body weight over 72 weeks, alongside a reduced-calorie diet and increased physical activity. At 10 mg, average loss was around 19.5%. At 5 mg, approximately 15%.
Wegovy (STEP trials): Participants on the maximum 2.4 mg dose lost an average of approximately 14.9% of body weight over 68 weeks, also with lifestyle changes. These are clinical trial averages — individual results vary significantly and are not assured.
Both medications are once-weekly injections, but Mounjaro uses the KwikPen device whilst Wegovy uses an auto-injection pen. Important: these trial results do not mean one is "better" — individual response differs, and prescriber assessment determines suitability.
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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.
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Mechanism, Doses, and Prescription Access
Mounjaro starts at 2.5 mg and escalates to a maximum of 15 mg over 20+ weeks. It activates both GIP and GLP-1 pathways, which may contribute to its average weight loss results in trials.
Wegovy starts at 0.25 mg and reaches a maximum of 2.4 mg over 16+ weeks. It activates GLP-1 only. Both are available through NHS specialist tier 3/4 weight management services (with significant regional variation and waiting lists) or through private prescription following an online clinical assessment. Access, cost, and availability differ by region and provider. Your GP or prescriber will discuss which medication, if either, is appropriate for your individual health profile.
- 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.
What is the main difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two hormone pathways. Wegovy (semaglutide) activates GLP-1 only. This dual mechanism may explain why Mounjaro showed higher average weight loss in clinical trials, but individual results vary significantly and prescriber assessment determines suitability.
How do I know which bundle or dose is right for me?
Both medications require prescription and a clinical assessment by a UK-licensed prescriber. They will review your health history, BMI, any weight-related conditions, and other medications to determine if either is suitable and at what starting dose. You cannot self-select doses — titration is managed by your prescriber over weeks.
Can I switch from Mounjaro to Wegovy or vice versa?
Switching between medications must be managed by your prescriber. There is no official established conversion chart — approximate equivalences exist (e.g., Mounjaro 15 mg ≈ Wegovy 2.4 mg), but any switch requires clinical oversight. Discuss with your prescriber if you experience side effects or have concerns.
Are Mounjaro bundles available on the NHS in the UK?
Mounjaro is approved by NICE for NHS use within specialist tier 3/4 weight management services. However, NHS availability, waiting lists, and bundle structures vary significantly by region (ICB). Many patients access Mounjaro through private prescription after online clinical assessment, which may be faster but involves out-of-pocket cost.
Which injection causes fewer side effects, Mounjaro or Wegovy?
Both have similar common side effects: nausea, diarrhoea, vomiting, constipation, and stomach pain — especially during dose escalation. Individual tolerability varies. Your prescriber will discuss side effect management and whether dose adjustments are needed. Track your progress and side effects using our free progress tracker to discuss with your prescriber at review appointments. ```
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