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 Speed Up Your Metabolism?
Mounjaro (tirzepatide) doesn't directly speed up your metabolism in the traditional sense. Instead, this prescription GLP-1 and GIP receptor agonist works by reducing your appetite, helping you feel fuller after eating smaller meals, and slowing how quickly food leaves your stomach. It's approved for weight management in UK adults meeting NHS eligibility criteria. Understanding how Mounjaro actually works—rather than expecting a metabolic boost—helps set realistic expectations for treatment with this medication.
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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 Actually Affects Your Body
Mounjaro is not a metabolism accelerator. It works through appetite suppression and hormone signalling, not by increasing calorie burn. The medication activates two pathways—GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1)—which together help regulate hunger signals in the brain, reduce cravings, and slow gastric emptying (digestion).
In clinical trials, participants taking Mounjaro at the maximum 15 mg dose lost an average of approximately 21% of their body weight. However, this weight loss came from eating fewer calories due to reduced appetite—not from the body burning more energy at rest. Weight loss happens because of a calorie deficit created by eating less, not metabolic acceleration. The medication also helps stabilise blood sugar levels, which can reduce energy crashes that often trigger overeating. Your GP or a specialist prescriber can explain how Mounjaro's mechanisms might work for your individual situation.
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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.
NHS Eligibility and Getting Mounjaro in the UK
In the UK, Mounjaro is available through NHS specialist tier 3 weight management services for adults with a BMI of 30 or above, or BMI of 27–29.9 with weight-related health conditions (type 2 diabetes, high blood pressure, heart disease). NICE has approved tirzepatide for NHS use, though regional availability varies significantly. Private access is available through GPhC-registered online pharmacies following a clinical assessment with a UK-licensed prescriber. Whichever route you choose, a prescriber will assess whether Mounjaro's appetite-suppressing effects are appropriate for your health profile. Try our GLP-1 weight loss calculator to estimate potential results, and use our BMI calculator to check your current classification.
- 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.
Will Mounjaro increase my metabolic rate or calorie burn?
No. Mounjaro doesn't directly increase your resting metabolic rate. Weight loss occurs because the medication reduces hunger and cravings, leading you to eat fewer calories. The calorie deficit you create by eating less is what drives weight loss, not a faster metabolism.
How much weight can I expect to lose with Mounjaro on the NHS?
Clinical trials (SURMOUNT-1) showed an average weight loss of approximately 15–21% of body weight over 72 weeks on Mounjaro, alongside a reduced-calorie diet and increased physical activity. Individual results vary significantly. Your prescriber will discuss realistic goals for your situation.
Is Mounjaro available on the NHS in the UK?
Yes. NICE has approved tirzepatide (Mounjaro) for NHS specialist weight management services (tier 3). Eligibility requires a BMI of 30 or above, or 27–29.9 with weight-related health conditions. Access varies by region and NHS waiting lists can be lengthy. Your GP can refer you to your local specialist service.
How does Mounjaro compare to Wegovy for weight loss?
Both are prescription-only weekly injections for weight management. Mounjaro (tirzepatide) uses a dual GIP+GLP-1 mechanism; Wegovy (semaglutide) is a single GLP-1 agonist. Clinical trials suggest similar average weight loss outcomes (approximately 15–21% for Mounjaro, approximately 15% for Wegovy), though results vary between individuals. Your prescriber will assess which is more suitable for you.
What are the most common side effects of Mounjaro in the UK?
Nausea, diarrhoea, vomiting, constipation, and stomach pain are very common, especially in the first few weeks. These often improve over time as your body adjusts. Less common side effects include injection site reactions, fatigue, and headache. Always report persistent or severe side effects to your prescriber.
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.