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 — UK Dose and Weight Loss Comparison
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription weight loss injections available in the UK, but they work differently and have different dosing schedules. If you're wondering how much Mounjaro is going up in cost or how it compares to Wegovy, understanding the key differences — from starting doses to clinical trial results — will help you and your GP or prescriber decide which might be suitable for you. This guide compares both medications factually, covering dose titration, weight loss outcomes, and access in the UK.
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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.
Clinical Trial Results and Dosing Differences
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways in the body. It starts at 2.5 mg and titrates up to a maximum of 15 mg once weekly. In the SURMOUNT-1 clinical trial, participants taking the highest dose (15 mg) achieved an average weight loss of approximately 20.9% of their body weight over 72 weeks, alongside a reduced-calorie diet and increased physical activity.
Wegovy (semaglutide) is a GLP-1 receptor agonist only — it activates one hormone pathway. It starts at 0.25 mg and titrates to a maximum of 2.4 mg once weekly. In the STEP-1 clinical trial, participants taking 2.4 mg achieved average weight loss of approximately 14.9% of their body weight over 68 weeks, also with lifestyle changes.
Both are prescription-only medicines requiring a clinical assessment. Individual results vary significantly, and weight loss is not assured. Use our free GLP-1 weight loss calculator to explore potential outcomes at different doses based on trial data.
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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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Access, Eligibility and Which Is Right for You
Eligibility for both Mounjaro and Wegovy in the UK is similar: adults with a BMI of 30 kg/m² or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. Both are available through NHS specialist weight management services (tier 3) or private online prescribing following a UK clinical assessment.
The choice between them depends on individual health factors, how your body responds, and prescriber recommendation — not on which is "better". Some people respond better to a dual-mechanism medication like Mounjaro; others do well on the single GLP-1 pathway with Wegovy. Your GP or prescriber will assess suitability based on your medical history, existing medications, and preferences. Use our free BMI calculator to check your current BMI and understand your eligibility status.
- 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 main difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) activates two hormone pathways — GIP and GLP-1 — while Wegovy (semaglutide) activates only GLP-1. This dual mechanism in Mounjaro may contribute to slightly higher average weight loss in clinical trials, but individual response varies. Both require prescription and clinical assessment.
How much weight can I expect to lose on Mounjaro vs Wegovy?
Clinical trials showed Mounjaro at 15 mg resulted in approximately 20.9% average body weight loss, and Wegovy at 2.4 mg resulted in approximately 14.9%. These are averages — individual results vary significantly. Your actual outcome depends on adherence, lifestyle changes, genetics, and how your body responds.
Is Mounjaro more expensive than Wegovy in the UK?
Private costs vary by provider and dose, typically ranging from £129–£320 per month for both medications. NHS access is free but involves waiting lists and regional variation. Mounjaro's higher maximum dose (15 mg vs Wegovy's 2.4 mg) means you may pay more for higher-dose pens privately, but both are accessible on the NHS through specialist services.
How do Mounjaro and Wegovy doses compare?
Mounjaro starts at 2.5 mg weekly (approximate equivalence: 5 mg ≈ 0.5 mg Wegovy, 10 mg ≈ 1.7 mg Wegovy, 15 mg ≈ 2.4 mg Wegovy). However, these are approximate only — switching between medications must be managed by your prescriber. Both are once-weekly injections.
Can I switch from Wegovy to Mounjaro or vice versa?
Yes, switching is possible, but it must be done under prescriber supervision. There is no official established conversion between the medications, so your prescriber will assess which approach is best for you. If one isn't working well, discussing an alternative with your GP or specialist is reasonable.
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