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 Guide
If you're considering switching from Mounjaro (tirzepatide) to Wegovy (semaglutide), you may wonder how the doses compare. While both are prescription-only weight loss injections used in the UK, they work differently and have different dose ranges. There is no official NHS conversion chart, but approximate equivalences exist based on clinical experience. Any switch between medications must be managed by your prescriber following a clinical assessment — never adjust doses yourself. This guide explains the approximate dose relationship and what you need to know about switching.
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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
Based on clinical trial data and prescribing practice, approximate dose equivalences exist between Mounjaro's tirzepatide and Wegovy's semaglutide, though these are not official NHS conversions:
- Mounjaro 5 mg (weekly) ≈ Wegovy 0.5 mg (weekly)
- Mounjaro 10 mg (weekly) ≈ Wegovy 1.7 mg (weekly)
- Mounjaro 15 mg (weekly) ≈ Wegovy 2.4 mg (weekly)
These equivalences are based on comparable weight loss outcomes in clinical trials — Mounjaro's SURMOUNT trial and Wegovy's STEP trials. However, individual response varies significantly. The drugs work through different mechanisms: Mounjaro is a dual GIP and GLP-1 receptor agonist, whilst Wegovy activates GLP-1 only. Your prescriber may not convert doses directly; instead, they may restart at a lower Wegovy dose and titrate upwards based on your individual tolerance and response. Any dose change requires a new clinical assessment and prescription.
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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 Doses Aren't Directly Equivalent
Although approximate equivalences help guide prescribers, direct dose conversion is not straightforward. Mounjaro's dual mechanism (activating both GIP and GLP-1 pathways) may produce stronger effects at lower doses compared to Wegovy's single GLP-1 mechanism. This means a patient on Mounjaro 10 mg may not achieve identical results on Wegovy 1.7 mg. Additionally, side effect tolerance differs between individuals and between the two medications. Your prescriber will consider your current dose, how well you've tolerated it, any side effects, and your weight loss progress before deciding how to switch. Using the GLP-1 weight loss calculator on this page can help you understand projected outcomes at different doses, though individual results always vary. A clinical assessment is essential before any medication switch.
- 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 to Wegovy at an equivalent dose?
Not without prescriber guidance. Whilst approximate equivalences exist (Mounjaro 10 mg ≈ Wegovy 1.7 mg), these are not official conversions. Your prescriber may restart you at a lower Wegovy dose due to different mechanisms and individual tolerance factors. Any switch requires a new clinical assessment and prescription.
Is Wegovy the same as Ozempic?
Both contain semaglutide, but Wegovy is licensed specifically for weight management in the UK (up to 2.4 mg weekly), whilst Ozempic is licensed for type 2 diabetes (up to 2 mg). Using Ozempic for weight loss is off-label. Wegovy is the authorised UK weight loss version.
Why is Mounjaro potentially more potent than Wegovy?
Mounjaro activates two hormone pathways (GIP and GLP-1), whilst Wegovy activates GLP-1 only. This dual mechanism may produce stronger appetite suppression and metabolic effects, meaning lower Mounjaro doses may achieve similar results to higher Wegovy doses. Clinical trials support this difference.
What happens if I'm on Mounjaro 15 mg and switch to Wegovy?
Your prescriber will likely start you on a lower Wegovy dose (perhaps 0.5 mg or 1 mg) and titrate upwards based on tolerance, rather than jumping to the 2.4 mg maximum. This gradual approach minimises side effects and allows your body to adjust to the different medication.
Can I use the GLP-1 weight loss calculator to compare Mounjaro and Wegovy?
The calculator on this page helps estimate weight loss outcomes with GLP-1 medications. Whilst Mounjaro is a GIP/GLP-1 agonist (potentially stronger), the calculator provides a useful reference point. Always discuss projected outcomes and medication choice with your prescriber during your clinical assessment.
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