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 Dose Conversion Chart
If you're switching from Mounjaro (tirzepatide) to Wegovy (semaglutide), understanding approximate dose equivalence can help your conversation with your GP or prescriber. Both are once-weekly injectable medications licensed for weight management in the UK, but they work slightly differently — Mounjaro is a dual GIP and GLP-1 receptor agonist, while Wegovy is a GLP-1 agonist only. There is no official NHS conversion chart, but approximate equivalences exist based on clinical practice. Always discuss any medication switch with your prescriber, as individual factors affect which dose is right for you.
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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
These approximate conversions are based on clinical practice guidance, not official NHS or pharmaceutical recommendations. Any switch between medications must be managed by your prescriber.
- Mounjaro 5 mg ≈ Wegovy 0.5 mg — Both are early escalation doses
- Mounjaro 10 mg ≈ Wegovy 1.7 mg — Mid-range therapeutic doses
- Mounjaro 15 mg (maximum) ≈ Wegovy 2.4 mg (maximum) — Full-dose equivalence
These are approximations only. Because Mounjaro's dual mechanism (GIP + GLP-1) is more potent than Wegovy's single GLP-1 mechanism, a lower Mounjaro dose may produce similar effects to a higher Wegovy dose. Your prescriber will assess your individual response and adjust accordingly. Switching medications may require a new KwikPen prescription and clinical reassessment.
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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.
Why Switching Between Medications Happens
People may switch from Mounjaro to Wegovy for several reasons: side effects, cost, availability, or individual response. Some NHS specialist weight management services may stock one medication but not the other, so a switch may be clinically necessary. Private prescribers may also recommend switching if the first medication isn't delivering expected results or is causing unmanageable side effects.
When switching, your prescriber may restart you on a lower dose of the new medication — even if you were on a higher dose of the previous one — to monitor your response and reduce side effect risk. You'll typically stay on the new medication for at least 4 weeks before any dose escalation. Keep a record of your weight loss progress using our free progress tracker to help your prescriber assess effectiveness.
- 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 an official Mounjaro to Wegovy conversion dose from NHS or MHRA?
No. MHRA and NHS have not published official conversion guidelines. Approximate equivalences come from clinical practice experience, not formal studies. Your prescriber will assess you individually and may not follow a direct conversion — they may start you at a lower dose and escalate based on your response and tolerance.
Why is Mounjaro sometimes more effective than Wegovy at lower doses?
Mounjaro is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways. Wegovy activates GLP-1 only. This dual mechanism may produce greater appetite suppression and weight loss at lower dose volumes, which is why approximate equivalence often shows Mounjaro 5 mg ≈ Wegovy 0.5–1 mg rather than exact numerical conversion.
Can I just switch Mounjaro KwikPens for Wegovy myself?
No. Both are prescription-only medications. You must get a new prescription from your GP or a UK-licensed prescriber. Your prescriber will assess whether switching is appropriate, review your health history, and issue the new prescription. Switching without clinical guidance could be unsafe.
Will I need to restart at a low Wegovy dose if I switch from Mounjaro 15 mg?
Possibly. Many prescribers restart at Wegovy 0.25 mg or 0.5 mg even if you were on maximum Mounjaro, to assess tolerance. This cautious approach reduces side effect risk and allows monitoring of your individual response. Escalation would then follow the standard Wegovy schedule (4 weeks per dose increase).
How can I track weight loss during a medication switch?
Use our free GLP-1 weight loss calculator to estimate potential outcomes on your new dose, and track actual progress with our free progress tracker. Weight loss often stabilises briefly after switching before resuming, so give the new medication at least 4–6 weeks before assessing effectiveness with your prescriber.
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.