The UK's most complete GLP-1 guide
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- 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 vs Wegovy — Dose Equivalent Guide
Mounjaro (tirzepatide) and Wegovy (semaglutide) are both prescription-only weight management injections licensed in the UK, but they work via different mechanisms and have different dose ranges. While approximate dose equivalences exist based on clinical practice, there is no official established conversion between them. This guide explains the dose relationship, how they differ, and how a prescriber determines the right dose for you.
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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 Dose Equivalence Chart
There is no official established conversion chart between Mounjaro and Wegovy doses. However, based on clinical practice guidance and the outcomes of their respective clinical trials (SURMOUNT for Mounjaro, STEP for Wegovy), approximate equivalences are often referenced:
- Mounjaro 5 mg ≈ Wegovy 0.5 mg (early escalation doses)
- Mounjaro 10 mg ≈ Wegovy 1.7 mg (mid-range maintenance)
- Mounjaro 15 mg ≈ Wegovy 2.4 mg (maximum doses)
These approximate equivalences are based on the weight loss outcomes observed in clinical trials, not on exact pharmacological equivalence. Individual response varies significantly. A prescriber assesses your suitability for each medication independently — switching between them requires clinical reassessment, not automatic dose conversion. Use our free GLP-1 weight loss calculator to explore projected outcomes at different doses for either medication.
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If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
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Why Mounjaro and Wegovy Are Not Directly Equivalent
Mounjaro (tirzepatide) and Wegovy (semaglutide) have different mechanisms of action. Mounjaro is a dual GIP and GLP-1 receptor agonist, activating two separate hormone pathways for appetite regulation. Wegovy is a GLP-1-only agonist, working through a single mechanism. Because they engage different biological pathways, the doses are not interchangeable on a 1:1 basis. Clinical trial data shows Mounjaro achieved slightly higher average weight loss than Wegovy at comparable time points, but individual results depend on your genetics, lifestyle, and adherence. Your GP or prescriber will assess which medication suits your health profile, UK eligibility status, and treatment goals — and which dose to start at — rather than converting between them.
- 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 from Mounjaro to Wegovy using an equivalent dose?
No. While approximate dose equivalences exist, any switch between medications requires a new clinical assessment from your prescriber. You cannot simply convert one dose to another — your prescriber will reassess your suitability and recommend an appropriate starting dose for the new medication, typically beginning at the lowest dose and escalating gradually.
What is the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) activates GIP and GLP-1 pathways (dual mechanism), while Wegovy (semaglutide) activates GLP-1 only. Mounjaro doses range from 2.5 mg to 15 mg weekly; Wegovy ranges from 0.25 mg to 2.4 mg weekly. Clinical trials showed Mounjaro achieved approximately 15–21% average weight loss, Wegovy approximately 15% — individual results vary significantly.
How long does it take to reach the maximum dose of either medication?
Mounjaro requires minimum 4 weeks at each dose level before escalating, so reaching 15 mg takes approximately 20 weeks. Wegovy requires 4-week escalation steps to reach 2.4 mg, taking approximately 16 weeks. Prescribers may extend timeframes if you experience side effects, prioritising safety over speed.
Which medication is available on the NHS in the UK?
Both Mounjaro and Wegovy are NICE-approved for NHS use within specialist tier 3/4 weight management services. Access varies significantly by region (ICB). Both are available privately through GPhC-registered online prescribers following clinical assessment. Waiting times for NHS access are often lengthy.
Can I use our GLP-1 calculator to compare projected outcomes between them?
Yes. Our free GLP-1 weight loss calculator allows you to explore projected weight loss at different doses for either medication. Individual results vary based on lifestyle, adherence, and personal factors — the calculator gives estimates only. Always discuss realistic expectations with your prescriber before starting treatment.
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