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
Free tracker included with every download this week
Does Mounjaro Burn Fat Or Just Suppress Appetite?
Mounjaro (tirzepatide) does both — it's not simply an appetite suppressant. As a dual GIP and GLP-1 receptor agonist, it works through multiple mechanisms: reducing hunger signals, slowing stomach emptying, and improving how your body uses fat and regulates blood sugar. Clinical trials showed an average weight loss of around 15–21% of body weight over 72 weeks, making it more effective than GLP-1-only medications like Wegovy. Understanding how Mounjaro actually works can help you and your GP decide if it's suitable for you. Use our free GLP-1 weight loss calculator above to explore potential outcomes at different doses.
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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 Differently
Mounjaro's dual mechanism: Mounjaro activates both GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 receptors. This means it targets two separate appetite and metabolic pathways simultaneously. The GIP component may enhance fat burning and reduce fat storage, whilst the GLP-1 component reduces appetite and slows gastric emptying. Together, these mechanisms support both appetite suppression and improved metabolic function.
Wegovy's single mechanism: Wegovy (semaglutide) activates GLP-1 receptors only. It primarily works by reducing hunger signals, making you feel fuller on smaller portions, and slowing how quickly food leaves your stomach. It does not directly target fat burning pathways.
SURMOUNT vs STEP trial results: Clinical trials (SURMOUNT-1 for Mounjaro, STEP-1 for Wegovy) showed Mounjaro delivered approximately 20.9% average weight loss at the maximum 15mg dose, compared to Wegovy's approximately 14.9% at 2.4mg — both over similar timeframes and alongside reduced-calorie diet and physical activity.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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 Assessment Matters
Both Mounjaro and Wegovy are prescription-only medicines requiring a clinical assessment before you can access them in the UK. Your prescriber will evaluate your BMI, weight-related health conditions (such as type 2 diabetes or high blood pressure), medical history, and current medications to determine which is more suitable. Neither medication is assured to work the same way for everyone — individual results vary significantly.
Use our free BMI calculator on this page to check your personal BMI, which is one of the first factors your GP or prescriber will assess. Both medications work best alongside a reduced-calorie diet, increased physical activity, and lifestyle changes. Your prescriber may also recommend starting at a lower dose and titrating up gradually to minimise side effects.
- 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 more fat than Wegovy?
Mounjaro's dual GIP+GLP-1 mechanism may support fat metabolism more directly than Wegovy's GLP-1-only mechanism. SURMOUNT trial data showed Mounjaro achieved approximately 20.9% average weight loss versus Wegovy's approximately 14.9%, but individual results vary significantly. Your prescriber will assess which is more suitable for you.
Can I switch from Wegovy to Mounjaro if Wegovy isn't working?
Switching between medications is possible but must be managed by your prescriber. Do not stop Wegovy and start Mounjaro yourself. Speak to your GP or the prescriber who issued your prescription about your concerns and whether switching is appropriate for your individual health situation.
How long does it take Mounjaro to start burning fat?
Weight loss typically becomes noticeable after 4–8 weeks, but some people see changes sooner or later. Fat loss is gradual and depends on maintaining a calorie deficit alongside the medication. Track your progress using our free progress tracker to monitor weight changes over time.
Is Mounjaro available on the NHS in the UK?
Mounjaro is approved by NICE for NHS use within specialist tier 3 weight management services. However, NHS availability varies significantly by region and waiting lists can be long. Private prescriptions are also available through UK-licensed online prescribers following a clinical assessment.
What are the main side effects of Mounjaro compared to Wegovy?
Both cause similar common side effects: nausea, diarrhoea, vomiting, and constipation — especially during dose titration. Mounjaro's dual mechanism may cause slightly different GI effects for some people. Side effects typically reduce as your body adjusts. Always inform your prescriber of any concerns.
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.