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 to Wegovy Conversion — What You Need to Know
Switching between Mounjaro (tirzepatide) and Wegovy (semaglutide) is a question many people ask, but there is no official one-to-one conversion chart. Both are prescription-only injectable weight loss medications, but they work differently and are prescribed at different dose ranges. Your prescriber will assess whether a switch is appropriate for your individual health needs, and if so, how to transition safely between them. This guide explains the approximate dose equivalence, the key differences between these two medications, and what to expect if you're considering making a change.
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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.
Approximate Mounjaro to Wegovy Dose Equivalence
There is no official NHS or MHRA conversion chart between Mounjaro and Wegovy, but clinical practice suggests approximate equivalence based on weight loss outcomes observed in clinical trials.
Based on SURMOUNT (Mounjaro) and STEP (Wegovy) trial data:
- Mounjaro 5 mg is roughly equivalent to Wegovy 0.5 mg — both are early escalation doses
- Mounjaro 10 mg is roughly equivalent to Wegovy 1.7 mg — mid-range maintenance doses
- Mounjaro 15 mg (maximum) is roughly equivalent to Wegovy 2.4 mg (maximum) — both achieve similar average weight loss of around 15–21% body weight
These are approximate guidelines only, not official conversions. Any actual switch must be managed by your prescriber, who will assess your individual response, current dose, and health status before recommending a transition plan.
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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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Why These Medications Are Different — And Why Switching Requires Clinical Input
Mounjaro (tirzepatide) and Wegovy (semaglutide) work through different mechanisms. Mounjaro is a dual GIP and GLP-1 receptor agonist, activating two separate hormone pathways, whilst Wegovy is a single GLP-1 receptor agonist. This dual mechanism is why Mounjaro may produce slightly more weight loss on average than Wegovy in clinical trials.
Because they work differently, you cannot simply swap the doses — individual response varies, and your prescriber will need to reassess you. Reasons to switch might include: side effects that are intolerable on one medication, improved access through a different provider, or clinical guidance based on your health conditions. Always discuss any medication change with your GP or prescriber before making decisions. If you're on the NHS, this conversation happens through your specialist weight management service.
- 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 I switch directly from Mounjaro 10 mg to Wegovy 1.7 mg without dose adjustment?
Not without your prescriber's guidance. While 10 mg Mounjaro and 1.7 mg Wegovy show similar average weight loss, individual response varies significantly. Your prescriber may recommend starting Wegovy at a lower dose and titrating up, or staying at 1.7 mg if you've tolerated Mounjaro well. The transition must be clinically managed, not self-directed.
Is Ozempic the same as Wegovy?
Both contain semaglutide, but they are not the same product. Ozempic is licensed for type 2 diabetes management (up to 2 mg) and is not approved for weight loss in the UK. Wegovy is the licensed weight management formulation (up to 2.4 mg). Using Ozempic for weight loss would be off-label and not recommended.
How long does it take to switch from Mounjaro to Wegovy?
The transition period depends on your prescriber's approach. You may stop Mounjaro and begin Wegovy at a starting dose, or there may be a brief gap. Wegovy starts at 0.25 mg and requires 4 weeks per dose before escalation, so reaching an equivalent dose level can take several months. Your prescriber will provide a personalised transition plan.
What if Wegovy doesn't work as well as Mounjaro for me?
Individual response to weight loss medication varies significantly. If Wegovy produces less weight loss or more side effects than you experienced on Mounjaro, discuss this with your prescriber. You may be able to return to Mounjaro or explore other options, depending on NHS availability or private access.
Can I use MyWeightCheck tools to track the switch between medications?
Yes. Our free GLP-1 weight loss calculator can help you estimate potential weight loss at different Wegovy doses, and our progress tracker allows you to log your weight throughout the transition period. Our BMI calculator also helps you monitor changes in your BMI as you progress with either medication.
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.