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 vs Wegovy: Dose Equivalents Explained
Mounjaro (tirzepatide) and Wegovy (semaglutide) are both prescription-only weight loss injections available in the UK, but they work differently and use different dosing schedules. While approximate dose equivalents exist, there is no official conversion chart between them — switching medications requires prescriber guidance. This guide compares their mechanisms, doses, and what the clinical trial data shows about outcomes.
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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.
How Mounjaro and Wegovy Differ: Mechanism and Dosing
Mounjaro is a dual GIP and GLP-1 receptor agonist — meaning it activates two natural hormone pathways — while Wegovy is a GLP-1 receptor agonist only, activating a single pathway. This fundamental difference means the medications work through slightly different mechanisms, which may affect how individual bodies respond.
Mounjaro uses a weekly injection starting at 2.5 mg and escalating to a maximum of 15 mg per week. Wegovy starts at 0.25 mg per week and escalates to a maximum of 2.4 mg per week — a much smaller absolute dose because semaglutide is more potent at lower concentrations. Each dose is adjusted gradually over weeks to allow the body to adapt and minimise gastrointestinal side effects. Our GLP-1 weight loss calculator can help you understand potential outcomes at different dose levels, and using our free BMI calculator alongside this information gives you a complete picture of where you stand health-wise before and during treatment.
- Mounjaro: Dual mechanism, larger dose range (2.5–15 mg), once weekly
- Wegovy: Single GLP-1 mechanism, smaller dose range (0.25–2.4 mg), once weekly
- Escalation time: Both take 4 weeks between dose increases
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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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Approximate Dose Equivalents and Clinical Trial Outcomes
Approximate dose equivalents are suggested in clinical practice, though no official NHS or MHRA conversion exists. Roughly: Mounjaro 5 mg ≈ Wegovy 0.5 mg; Mounjaro 10 mg ≈ Wegovy 1.7 mg; Mounjaro 15 mg ≈ Wegovy 2.4 mg. However, these are clinical approximations only, not interchangeable.
In the SURMOUNT-1 trial, Mounjaro showed average weight loss of 20.9% at the 15 mg dose over 72 weeks. In the STEP-1 trial, Wegovy showed average weight loss of 14.9% at 2.4 mg over 68 weeks. Individual results vary significantly and are achieved alongside reduced-calorie diet and increased physical activity. Both medications require a UK-licensed prescriber assessment to determine which is suitable for your individual health profile, medical history, and eligibility.
- 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 without stopping?
Any switch between weight loss medications must be managed by your prescriber. There is no standard protocol for switching — your prescriber will advise on the safest approach for your individual circumstances. Do not stop one medication and start another without medical guidance.
Which has fewer side effects — Mounjaro or Wegovy?
Both medications have similar common side effects: nausea, diarrhoea, vomiting, constipation, and stomach pain are very common with both. Individual tolerance varies. Your prescriber can discuss which medication's side effect profile may suit you better based on your medical history.
Is Mounjaro more effective than Wegovy because it's a dual mechanism?
In clinical trials, Mounjaro showed slightly higher average weight loss percentages than Wegovy. However, this does not mean it is "better" — individual results vary widely, and suitability depends on your health conditions, medications, and prescriber assessment, not just average trial data.
How do I know which dose of Mounjaro or Wegovy is right for me?
Dosing is determined by your prescriber following a clinical assessment. Your GP or specialist will consider your BMI, weight-related health conditions, medical history, and other medications. You typically start at the lowest dose and increase gradually as tolerated. Use our BMI calculator to understand your starting BMI context.
Are Mounjaro and Wegovy available on the NHS in the UK?
Both are approved for NHS use through tier 3 specialist weight management services, but availability varies significantly by region and waiting lists can be lengthy. Private prescribing is also available through GPhC-registered online services following a clinical assessment with a UK-licensed prescriber.
Ready to take control of your weight loss journey?
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