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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Switching To Wegovy From Mounjaro: NHS And UK Prescribing Guide
If you're considering switching from Mounjaro (tirzepatide) to Wegovy (semaglutide), there's no official UK conversion chart—but your prescriber can guide you through a safe transition. Both are GLP-1 based weight loss injections, but they work differently. This guide explains NHS eligibility, how the switch works in practice, and what to expect when moving between these prescription-only medications. Your GP or specialist will assess whether switching is appropriate 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.
NHS Eligibility And The Prescribing Pathway For Wegovy
In the UK, Wegovy (semaglutide) is approved for weight management in adults with a BMI of 30 or above, or BMI 27–29.9 with a weight-related health condition such as type 2 diabetes, high blood pressure, or cardiovascular disease. For people of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds may apply (starting from BMI 27.5 or above).
Access via the NHS is through specialist tier 3 weight management services—not standard GP prescriptions. You'll need referral from your GP, clinical assessment by a specialist team, and ongoing monitoring. Regional variation is significant; some areas have substantial waiting lists. If you're already on Mounjaro through the NHS, switching to Wegovy would typically involve discussion with your specialist service. NICE has approved both medications, but availability depends on your local Integrated Care Board (ICB) commissioning decisions and current service capacity.
The STEP clinical trials demonstrated Wegovy's effectiveness: approximately 14.9% average weight loss over 68 weeks at the maximum 2.4 mg dose, alongside reduced-calorie diet and increased physical activity. Individual results vary considerably.
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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.
Switching From Mounjaro To Wegovy: Practical Considerations
There is no official established dose conversion between Mounjaro (tirzepatide, dual GIP+GLP-1 agonist) and Wegovy (semaglutide, GLP-1 agonist only). Approximate clinical equivalences exist—for example, Mounjaro 10 mg is sometimes considered roughly equivalent to Wegovy 1.7 mg—but these are not fixed prescribing standards.
Your prescriber will typically restart at Wegovy's starting dose (0.25 mg) and titrate upwards over weeks, even if you were on a higher Mounjaro dose. This allows your body to adjust to the different medication profile. You may experience different side effects; nausea and gastrointestinal effects can feel new or different despite both being GLP-1 based. Track your response using our free progress tracker to monitor how the switch affects your weight loss journey. Switching between medications should only happen under prescriber guidance—never stop one and start another without clinical support.
NHS Versus Private Routes For Accessing WegovyNHS route: Referral through GP to tier 3 specialist weight management service, assessment, prescription, and ongoing monitoring. Free at point of use but subject to waiting lists and regional commissioning decisions. Some ICBs commission Wegovy; others prioritise Mounjaro or older medications. Availability varies dramatically across the UK.
Private route: Online consultation with a UK-licensed prescriber, prescription issued if clinically appropriate, dispensed by a GPhC-registered pharmacy. Available without NHS referral, typically faster than NHS routes, costs approximately £129–£300 per month depending on dose. You can use our GLP-1 weight loss calculator to estimate potential outcomes at different Wegovy doses and discuss these projections with your prescriber during assessment. Always ensure any private prescriber is registered with the General Medical Council (GMC) and fully qualified to prescribe weight management medications in the UK.
- 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 my GP prescribe Wegovy directly, or do I need a specialist referral?
Wegovy is typically prescribed through NHS specialist tier 3 weight management services, not standard GP prescription. You'll need referral from your GP to your local specialist service. However, private online prescribers can issue Wegovy prescriptions following an online clinical assessment without NHS referral—though they must be UK-licensed and GMC-registered.
Is there a dose conversion from Mounjaro to Wegovy?
There is no official NHS or MHRA conversion chart. Approximate equivalences exist (e.g., Mounjaro 10 mg ≈ Wegovy 1.7 mg), but prescribers typically restart at Wegovy's starting dose (0.25 mg) and titrate upwards. Your prescriber will manage the transition based on your individual response and tolerability.
Will I experience different side effects if I switch from Mounjaro to Wegovy?
Possibly. Both medications cause similar common side effects (nausea, diarrhoea, constipation, reduced appetite), but because Wegovy is a single GLP-1 agonist (versus Mounjaro's dual GIP+GLP-1 mechanism), the exact profile may differ. Some people tolerate one better than the other. Nausea typically improves over weeks as your body adjusts.
How long does the switch take, and will I have a gap without medication?
Transition timing depends on your prescriber. Some coordinate an overlap; others may have a brief gap. Your specialist or prescriber will explain their approach. Generally, starting Wegovy at 0.25 mg and titrating over 4–5 weeks to reach an effective dose takes approximately 16–20 weeks to reach maximum dose (2.4 mg).
Can I use tools to track my weight loss progress on Wegovy?
Yes. MyWeightCheck's free progress tracker lets you log your weight, monitor trends, and see visual progress over time—helpful for assessing how Wegovy is working for you. Our BMI calculator also lets you track changes in your BMI as you lose weight, and our weight converter helps you track progress in your preferred units (kg, stone, or lbs).
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.