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?
Yes, it is possible to switch from Mounjaro (tirzepatide) to Wegovy (semaglutide) in the UK, but it requires careful medical supervision and a prescription from your GP or a licensed prescriber. Both are GLP-1 receptor agonist medications for weight management, but they work differently and have different dose ranges. Any transition must be managed individually based on your health, current dose, and response to treatment. This guide explains what you need to know about switching between these two weight loss injections.
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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.
How Mounjaro and Wegovy Differ
Mounjaro is a dual GIP and GLP-1 receptor agonist — it activates two hormone pathways simultaneously, which may help suppress appetite more strongly. The tirzepatide dose range is 2.5 mg to 15 mg once weekly via a KwikPen.
Wegovy is a GLP-1-only receptor agonist containing semaglutide. It activates a single hormone pathway and has a maximum dose of 2.4 mg once weekly. Clinical trials (STEP-1) showed average weight loss of approximately 15% body weight, though individual results vary significantly.
Because they work by different mechanisms and have different potencies, there is no direct one-to-one dose conversion between them. A Mounjaro dose of 5 mg is approximately equivalent to Wegovy 0.5 mg, 10 mg Mounjaro to roughly 1.7 mg Wegovy, and 15 mg Mounjaro to 2.4 mg Wegovy — but these are estimates only. Your prescriber will assess your individual situation and may start you on a lower Wegovy dose even if you were stable on a higher Mounjaro dose, because the single GLP-1 mechanism works differently.
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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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What Your GP or Prescriber Needs to Know
If you want to switch to Wegovy, inform your prescriber about your current Mounjaro dose, how long you have been taking it, how well it has worked for you, and any side effects you have experienced. You will need a new prescription because Wegovy and Mounjaro are separate medications.
Your prescriber may suggest a gradual transition or may recommend stopping Mounjaro before starting Wegovy. There is no standard "switchover protocol" — each transition is individualised. You cannot simply switch pens; each medication must be prescribed separately. If you are accessing treatment through the NHS, your specialist weight management service will manage the switch. If using private prescribing, contact your prescriber for guidance before making any changes. Never stop Mounjaro without medical advice.
- 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 there a standard dose conversion from Mounjaro to Wegovy?
No official conversion exists. Approximate rough equivalents are: 5 mg Mounjaro ≈ 0.5 mg Wegovy, 10 mg ≈ 1.7 mg, and 15 mg ≈ 2.4 mg. However, your prescriber may start you on a lower Wegovy dose because the single GLP-1 mechanism differs from Mounjaro's dual GIP/GLP-1 action. Individual assessment is essential.
Will I lose more weight on Wegovy than Mounjaro?
Clinical trials show slightly lower average weight loss with Wegovy (~15%) versus Mounjaro (~21% at highest dose). However, individual results vary greatly — some people respond better to one medication than the other. Your previous response to Mounjaro does not assures the same result with Wegovy.
Can I switch immediately from Mounjaro to Wegovy?
Not without medical guidance. Your prescriber may recommend a washout period (stopping Mounjaro for several days) before starting Wegovy, or a direct transition. Switching without medical supervision risks either a gap in treatment or overlapping medications, both potentially unsafe.
Will my side effects change if I switch to Wegovy?
Possibly. Both medications cause similar side effects (nausea, diarrhoea, constipation), but the GLP-1-only mechanism of Wegovy may cause different symptom severity or duration compared to Mounjaro's dual action. Some people tolerate one better than the other.
Can I access Wegovy on the NHS after Mounjaro?
NHS access depends on your local specialist weight management service and their current pathways. Some services may support switching between medications; others may have specific protocols. Contact your GP or specialist service to discuss options. Private prescribing is an alternative if NHS access is limited.
Ready to take control of your weight loss journey?
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