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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Can You Switch From Mounjaro to Wegovy in the UK?
Yes, you can move from Mounjaro to Wegovy in the UK, but the process depends on where you're currently receiving treatment. Both medications are prescription-only and require clinical assessment. If you're on Mounjaro through an NHS specialist service, switching would typically involve discussion with your specialist team. If you're receiving Mounjaro privately, you can request to switch to Wegovy with a new online clinical assessment. This guide explains the cost, access routes, and what to expect when moving between these two weight loss injections in the UK.
10,000+ calculations today ยท NHS-aligned thresholds ยท 100% free
Calculate Your BMI Instantly
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/mยฒ).
While BMI isn't a perfect measure โ it doesn't account for muscle mass, bone density, or fat distribution โ 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 โ 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.
Mounjaro vs Wegovy: Cost and Prescription Routes in the UK
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are licensed for weight management in the UK and available through NHS specialist services or private online prescribing. Costs differ significantly between routes:
Private prescription costs (typical monthly ranges):
- Mounjaro: ยฃ160โยฃ280 per month depending on dose
- Wegovy: ยฃ130โยฃ240 per month depending on dose
Actual costs vary by provider and dose โ starting doses (Mounjaro 2.5 mg, Wegovy 0.25โ0.5 mg) are often cheaper than maintenance or maximum doses. The mounjaro kwikpen device contains 4 weeks of doses, while Wegovy pens also contain a month's supply. Neither medication is available on prescription through standard NHS GP services โ only through tier 3 specialist weight management services, where availability varies significantly by region and can involve waiting lists of several months or longer.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care โ from a UK-regulated online pharmacy.
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 โ 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 โ completely free.
How to Switch: NHS vs Private Routes
If you're on Mounjaro through the NHS, discuss switching with your specialist team โ they may support a change or recommend continuing Mounjaro based on your response. Private prescription switching is straightforward: contact a UK GPhC-registered online prescriber, complete a new health assessment, and if approved, you'll receive a Wegovy prescription. The switch doesn't require permission from your current provider if you're on private treatment. Many people compare the two medications' side effects, tolerability, and results before deciding to switch. Our GLP-1 weight loss calculator can help you understand projected outcomes at different doses of either medication, though individual responses vary significantly. Allow 1โ2 weeks between stopping one medication and starting the other โ your prescriber will advise on timing.
- 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 โ 5mg โ 7.5mg โ 10mg โ 12.5mg โ 15mg
- GLP-1 receptor agonist
- Up to 15โ17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg โ 0.5mg โ 1mg โ 1.7mg โ 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 | 15โ22.5% | 12โ17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20โ32 weeks | 16โ20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | ยฃ150โยฃ250/month | ยฃ150โยฃ300/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 โ 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 Wegovy cheaper than Mounjaro in the UK?
Costs are similar but Wegovy is often slightly cheaper, typically ยฃ130โยฃ240 per month on private prescription versus Mounjaro at ยฃ160โยฃ280. Both vary by dose and provider. NHS costs are the same for both (covered by specialist services where available). Direct comparison depends on which doses you're taking.
Can I switch from Mounjaro to Wegovy on the NHS?
Yes, if you're receiving Mounjaro through an NHS tier 3 specialist service, discuss switching with your specialist team. They'll assess whether Wegovy is appropriate for you based on your individual response to Mounjaro and clinical need. NHS switching is based on clinical suitability, not cost.
How long should I wait between stopping Mounjaro and starting Wegovy?
Allow 1โ2 weeks between stopping Mounjaro and starting Wegovy. Both are GLP-1-based medications, so there's minimal washout needed. Your prescriber will provide specific timing guidance based on your individual circumstances.
What's the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist; Wegovy (semaglutide) is a GLP-1 agonist only. Mounjaro has two active mechanisms, which may explain slightly higher average weight loss in clinical trials. Both require weekly injections and are prescription-only. Switching allows you to try the alternative if one isn't suiting you.
Will I lose weight faster on Wegovy than Mounjaro?
No โ clinical trials show similar average weight loss for both medications (around 14โ21% body weight). Individual results vary significantly based on genetics, lifestyle, and adherence. Some people respond better to Mounjaro's dual mechanism; others do equally well on Wegovy's single mechanism. Your prescriber can help you choose based on your specific situation. ```
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.