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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Does Mounjaro Burn Fat — How It Works vs Wegovy
Mounjaro doesn't directly "burn" fat in the traditional sense, but it does help your body use fat differently by activating two natural hormone pathways. Understanding how Mounjaro works compared to Wegovy can help you and your GP decide which prescription weight loss treatment might suit you best. Both are once-weekly injections licensed in the UK for weight management, but they work through different mechanisms. Clinical trial data from the SURMOUNT and STEP studies shows meaningful weight loss outcomes with both medications, though individual results vary significantly.
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Calculate Your BMI Instantly
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.
How Mounjaro and Wegovy Work — The Science Behind Fat Loss
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways that regulate appetite, blood sugar, and fat utilisation. The GIP pathway specifically may enhance how your body processes and stores fat, whilst the GLP-1 component reduces hunger and cravings. In the SURMOUNT-1 trial, adults taking Mounjaro at the maximum 15 mg dose lost an average of 20.9% of their body weight over 72 weeks alongside a reduced-calorie diet and increased physical activity.
Wegovy (semaglutide) activates only the GLP-1 pathway, which signals fullness to your brain and slows gastric emptying. Whilst highly effective, it uses a single mechanism. STEP-1 trial data showed Wegovy achieved approximately 14.9% average weight loss at the maximum 2.4 mg dose over 68 weeks with the same lifestyle support.
Neither medication actively "burns" fat through metabolic acceleration—instead, both work by reducing calorie intake through appetite regulation, which creates the deficit needed for fat loss. The difference is that Mounjaro's dual action may provide additional metabolic support.
Clinically BackedWeight Loss
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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.
Which Is Right for You — Individual Suitability and NHS Access
Choosing between Mounjaro and Wegovy is not a personal preference—it's a clinical decision made by a GP or licensed prescriber following assessment of your individual health, BMI, medical history, and any existing conditions. Both require UK prescription and are available through NHS tier 3 specialist weight management services (with significant regional variation and waiting lists) or through private online prescribing following clinical assessment.
Eligibility for both medications is the same: BMI 30 or above, or BMI 27–29.9 with weight-related health conditions such as type 2 diabetes, hypertension, or cardiovascular disease. Use our free BMI calculator above to check your current BMI, and our GLP-1 weight loss calculator to see projected outcomes at different doses. Your GP can assess which medication's mechanism suits your individual circumstances best.
- 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.
Does Mounjaro actually burn fat or does it just reduce appetite?
Mounjaro reduces appetite primarily, but its dual GIP+GLP-1 mechanism may also enhance fat utilisation and metabolism more than GLP-1-only medications. Clinical trials show meaningful fat loss, though this results mainly from eating fewer calories (appetite reduction) rather than increased metabolic "burning."
Is Mounjaro more effective than Wegovy for fat loss?
SURMOUNT trial data showed slightly higher average weight loss with Mounjaro (20.9% vs Wegovy's 14.9%), but this is population average—individual results vary greatly. Effectiveness depends on your personal response, adherence, diet, and exercise, not just the medication.
How does Mounjaro's KwikPen work and does the dose affect fat loss?
Mounjaro is a pre-filled once-weekly injection pen. Doses range from 2.5 mg to 15 mg. Higher doses generally produce greater weight loss in trials, but prescribers titrate gradually (increasing every 4 weeks) to manage side effects. Your GP adjusts based on your tolerance and response.
Can I get Mounjaro on the NHS in the UK?
Yes, Mounjaro is NICE-approved and available through NHS tier 3 specialist weight management services, but regional availability varies significantly and waiting lists are often lengthy. Private prescription through a licensed UK prescriber is an alternative without NHS referral.
What should I consider when choosing between Mounjaro and Wegovy?
Both require prescription and clinical assessment. Your prescriber will consider your BMI, health conditions, medication interactions, tolerability, and whether the dual-mechanism approach (Mounjaro) or single GLP-1 pathway (Wegovy) suits you. Individual suitability matters more than which is "better."
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.