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 — How Much Do They Differ?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight management injections available in the UK, but they work differently and have different dose ranges. This guide explains the key differences in how much medication you'd take, how they work, and what clinical trials showed about weight loss results. Understanding these distinctions helps your GP or prescriber decide which option might be suitable for you. Both require a clinical assessment before prescription.
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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.
Dose Ranges and Expected Weight Loss Results
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — meaning it activates two hormone pathways. Starting dose is 2.5 mg weekly, escalating by 2.5 mg every four weeks up to a maximum of 15 mg weekly. The SURMOUNT-1 clinical trial showed average weight loss of approximately 15% body weight at 5 mg, 19.5% at 10 mg, and 20.9% at 15 mg over 72 weeks alongside diet and exercise changes.
Wegovy (semaglutide) is a single GLP-1 receptor agonist. It starts at 0.25 mg weekly, escalating every week to 0.5 mg, 1 mg, 1.7 mg, and reaching maximum 2.4 mg by week 17. The STEP-1 clinical trial showed average weight loss of approximately 14.9% body weight at 2.4 mg over 68 weeks with lifestyle changes.
These are averages — individual results vary significantly based on lifestyle, genetics, and how your body responds to the medication.
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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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Mechanism Differences and Suitability
The main difference is that Mounjaro acts on two hormone pathways (GIP and GLP-1) whilst Wegovy targets only GLP-1. This dual action in Mounjaro may produce slightly higher average weight loss in trials, but both medications help reduce appetite and support feeling fuller after smaller meals. Your GP or prescriber will assess which suits you based on your individual health profile, existing medications, and medical history. Neither is universally "better" — suitability depends on you. Both require a prescription from a UK-licensed prescriber following a clinical assessment.
- 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.
What's the difference between Mounjaro and Wegovy doses?
Mounjaro starts at 2.5 mg weekly and escalates to 15 mg maximum. Wegovy starts at 0.25 mg weekly and reaches 2.4 mg maximum. The doses are not directly comparable because they are different medications — approximate equivalence might be Mounjaro 5 mg ≈ Wegovy 0.5 mg, but any switch requires prescriber guidance.
Which causes more weight loss — Mounjaro or Wegovy?
Clinical trials showed Mounjaro at 15 mg achieved approximately 20.9% average weight loss, whilst Wegovy at 2.4 mg achieved approximately 14.9%. However, these are trial averages with lifestyle changes included. Individual results vary significantly — some people lose more on Wegovy, others on Mounjaro.
How do I know which one is right for me?
A UK-licensed prescriber will assess your medical history, existing medications, health conditions, and personal preferences. Both require a clinical assessment. Your GP can refer you to NHS specialist services, or you can access private prescribing through online services. The prescriber will recommend the most suitable option for your circumstances.
Can I switch from Mounjaro to Wegovy or vice versa?
Yes, switching is possible but requires prescriber guidance. There is no official established conversion chart — any switch must be managed individually. You cannot simply replace one dose with another; your prescriber will determine the appropriate starting point and escalation schedule.
Do both medications work the same way?
Not exactly. Mounjaro activates two hormone pathways (GIP and GLP-1), whilst Wegovy activates only GLP-1. Both reduce appetite and slow stomach emptying, but the dual mechanism in Mounjaro may explain slightly higher average trial weight loss. Both are prescription-only and require clinical assessment before use.
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.