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: Comparing Weight Loss Mechanisms
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription weight loss injections licensed in the UK, but they work slightly differently. Mounjaro is a dual GIP and GLP-1 receptor agonist, while Wegovy is a GLP-1 receptor agonist only. This means Mounjaro activates two hormone pathways whereas Wegovy activates one. Understanding how each medication affects appetite, calorie intake, and weight loss can help you and your prescriber decide which might be suitable for you. Both require a clinical assessment before prescription, and both are most effective when used alongside a reduced-calorie diet and increased physical activity.
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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: SURMOUNT vs STEP Results
Mounjaro (SURMOUNT-1 trial): At the maximum dose of 15 mg per week, participants lost an average of 20.9% of their body weight over 72 weeks. At 10 mg, average loss was approximately 19.5%, and at 5 mg around 15%. These results were achieved alongside a reduced-calorie diet and increased physical activity.
Wegovy (STEP-1 trial): At the maximum dose of 2.4 mg per week, participants lost an average of 14.9% of body weight over 68 weeks, also with dietary and lifestyle changes included.
Important context: individual results vary significantly. These are clinical trial averages, not assured outcomes. Some people lose more, some lose less. Try our GLP-1 weight loss calculator above to see projected weight loss estimates at different doses based on your starting weight, though actual results depend on your personal circumstances and adherence to lifestyle changes.
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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.
Mechanism Differences: How Each Medication Works
Mounjaro (dual mechanism): Activates both GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 receptors. This dual action may provide stronger appetite suppression and enhanced control of food cravings. The GIP pathway also helps with fat metabolism.
Wegovy (single mechanism): Activates GLP-1 receptors only. This still supports appetite reduction and feeling fuller after smaller meals, but through a single pathway.
Neither medication is insulin. Both slow gastric emptying (how quickly food leaves your stomach), though this effect typically lessens over time. Both also support reduced calorie intake — clinical trials show participants naturally eat fewer calories without strict calorie counting, though food choices and portion sizes still matter.
- 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.
How does Mounjaro affect calorie intake compared to Wegovy?
Clinical data suggests Mounjaro may produce greater average weight loss (up to 20.9% vs 14.9% in trials), which indicates stronger appetite suppression overall. However, both medications work by reducing hunger and cravings, allowing most people to eat smaller portions naturally. Individual response varies significantly — some people respond equally well to either medication.
Can I switch from Wegovy to Mounjaro if Wegovy isn't working for me?
Yes, switching between medications is possible and managed by your prescriber. Approximate dose equivalences exist (e.g., Wegovy 2.4 mg roughly correlates to Mounjaro 10-15 mg), but any switch must be discussed with your GP or prescriber based on your individual response and health circumstances. There is no official NHS conversion chart — your prescriber will assess the best approach.
Do both medications reduce calorie intake the same way?
Both reduce calorie intake by decreasing appetite, reducing food cravings, and increasing satiety (feeling full). Mounjaro's dual mechanism (GIP + GLP-1) may produce a slightly stronger appetite-suppressing effect based on clinical trials, but both medications work alongside lifestyle changes. Calorie reduction is not automatic — you still need to make healthier food choices.
Which medication will help me lose more weight?
Based on clinical trials, Mounjaro showed greater average weight loss than Wegovy. However, "which is better" depends entirely on your individual circumstances. Some people respond better to one medication than the other. Your prescriber will assess which is more suitable based on your health profile, medical history, and eligibility. Both require prescription and clinical assessment.
Can I use a calorie calculator with these medications?
Yes. Although these medications reduce hunger naturally, tracking food intake can still be helpful. Use our free BMI calculator and GLP-1 weight loss calculator to understand your current weight status and projected outcomes. Your GP or prescriber can also refer you to dietetic support for personalised calorie guidance alongside medication.
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.