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 From Wegovy To Mounjaro In The UK
Many UK adults on Wegovy (semaglutide) are asking about switching to Mounjaro (tirzepatide), particularly given differences in cost, availability, and how they work. Both are prescription-only weight management injections, but accessing either one involves different routes depending on whether you go through the NHS or private prescribing. This guide explains what you need to know about switching between them, the costs involved, and how to access both medications in the UK.
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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.
Understanding Cost And Access Routes In The UK
Both Wegovy and Mounjaro are available in the UK through two main routes: NHS specialist tier 3 weight management services, or private online prescription following a clinical assessment. NHS access is typically free at point of use but involves a GP referral to a specialist service and can have significant waiting lists—some regions have waiting times exceeding 18 months. Private prescription costs vary by dose and provider, typically ranging from £129 to £320 per month for either medication. Switching between medications privately is usually straightforward—your prescriber can assess whether Mounjaro is suitable based on your individual response to Wegovy. If you've experienced side effects on Wegovy or feel it's not working optimally, a clinical assessment can help determine if Mounjaro's dual GIP and GLP-1 mechanism might be more effective for you. NHS switches are more complex and depend on your specialist service's protocols and availability.
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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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Switching From Wegovy: What To Expect
If you're considering switching from Wegovy to Mounjaro, your first step is a fresh clinical assessment—either with your GP if pursuing NHS referral, or with a UK-licensed prescriber through private online consultation. Mounjaro starts at a lower dose (2.5 mg) than Wegovy's maximum, so there is no direct one-to-one dose conversion. Your prescriber will typically restart you on the initial dose and titrate upward over 16+ weeks. You may experience a temporary increase in appetite during the transition period as you move away from Wegovy and before Mounjaro reaches therapeutic levels. Keep a record of your weight using our free progress tracker to monitor how you respond to the new medication. Some people find Mounjaro's dual-action approach produces better results; others see similar outcomes. Individual responses vary significantly, so realistic expectations and patience through the titration phase are important.
- 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.
Is switching from Wegovy to Mounjaro available on the NHS?
Switching between weight loss medications on the NHS is possible but depends entirely on your local specialist tier 3 service and their protocols. Some services may support a switch if Wegovy hasn't worked well for you; others may require you to complete Wegovy first. Contact your specialist service directly to discuss your options.
How much does a private Mounjaro prescription cost compared to Wegovy?
Private costs for both medications are similar—typically £129 to £320 per month depending on the dose. Mounjaro's maximum dose (15 mg) and Wegovy's maximum dose (2.4 mg) cost roughly the same at most private providers. Exact pricing varies by provider, so compare quotes.
Will I have withdrawal symptoms if I stop Wegovy to switch to Mounjaro?
No formal withdrawal syndrome exists, but you may experience a temporary increase in appetite as your body adjusts. The transition is smoother if your prescriber starts you on Mounjaro immediately after your last Wegovy dose, minimising the gap between medications.
Can I switch doses instantly or do I need to retitrate?
Mounjaro requires a fresh titration schedule starting at 2.5 mg, even if you were on a high Wegovy dose. This typically takes 16–20 weeks to reach a maintenance dose. Skipping titration steps increases the risk of side effects and isn't recommended.
What should I tell my prescriber when discussing a switch?
Provide details of your Wegovy experience: current dose, how long you've been on it, weight loss achieved, any side effects, and why you want to switch. This helps your prescriber decide if Mounjaro's different mechanism (dual GIP/GLP-1 vs single GLP-1) is likely to suit you better. Try our GLP-1 weight loss calculator to compare projected outcomes at different doses.
Ready to take control of your weight loss journey?
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