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: Weight Tracking and Comparison
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription weight loss injections available in the UK, and both can be tracked using a weight management approach. The main difference is their mechanism: Mounjaro is a dual GIP and GLP-1 receptor agonist, while Wegovy works as a GLP-1 agonist only. Clinical trials showed different average weight loss outcomes, but individual results vary significantly. Your GP or prescriber will help determine which, if either, is suitable for your specific health needs following a clinical assessment. Tracking progress accurately is essential with either medication.
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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 Data and How They Compare
Mounjaro (tirzepatide) was tested in the SURMOUNT-1 trial. At the maximum 15 mg weekly dose, participants lost an average of approximately 20.9% of their body weight over 72 weeks, alongside a reduced-calorie diet and increased physical activity.
Wegovy (semaglutide) was tested in the STEP-1 trial. Participants on the maximum 2.4 mg weekly dose lost an average of approximately 14.9% of body weight over 68 weeks, also with dietary and lifestyle changes.
These are clinical trial averages — individual outcomes vary considerably. Mounjaro's dual GIP+GLP-1 mechanism differs from Wegovy's single GLP-1 pathway. Mounjaro starts at 2.5 mg and escalates to a maximum of 15 mg, while Wegovy escalates from 0.25 mg to 2.4 mg. Both are weekly weight loss injections delivered via pre-filled pens.
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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.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Tracking Progress and Choosing the Right Option
Whether you're tracking Mounjaro or Wegovy progress, consistent weekly weigh-ins help monitor how the medication supports your weight management goals. Use our free GLP-1 weight loss calculator to estimate potential weight loss at different doses, and the weight converter to track your weight in stone, pounds, or kilograms — whichever you prefer.
The choice between Mounjaro and Wegovy is individualised. Your prescriber will consider your health history, BMI, any weight-related conditions, and how your body responds during dose titration. Both require a UK prescription and clinical assessment. Availability on the NHS varies by region through specialist tier 3 weight management services; both are also available privately through online clinical assessments. Neither medication is a standalone solution — both work best alongside dietary changes and increased physical activity.
- 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 for weight loss?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways. Wegovy (semaglutide) is a GLP-1-only agonist. This mechanism difference may contribute to different average weight loss outcomes between the two, though individual results vary. Both are prescription-only UK weight loss injections.
Can I track my progress the same way with both medications?
Yes. Weekly weigh-ins are the standard approach for tracking progress with either medication. Use our free progress tracker to log your weight loss journey. Both Mounjaro and Wegovy are dosed and escalated over weeks, so tracking weekly or bi-weekly helps you and your prescriber monitor how the dose is working for you.
Which weight loss injection is more effective?
Clinical trials showed different average outcomes — Mounjaro showed higher average weight loss (approximately 20.9% at maximum dose) than Wegovy (approximately 14.9%) in their respective trials. However, individual results vary significantly. Your prescriber will assess which medication is more suitable for your personal health profile, not based on superiority but on individualised suitability.
How do I get Mounjaro or Wegovy prescribed in the UK?
Both are prescription-only and require a clinical assessment. You can access them via the NHS through a referral to a tier 3 specialist weight management service (availability varies by region), or privately through an online consultation with a UK-licensed prescriber. Your GP can discuss which route is appropriate for you.
Do I need to use a special weight tracker app with these injections?
No specific app is required. A simple weekly weigh-in using a reliable set of scales is sufficient. Use our free progress tracker on MyWeightCheck to log your weight in stone, pounds, or kilograms and monitor trends over weeks and months. Consistent tracking helps you and your prescriber assess how the medication is supporting your weight management.
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.