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, it works through a dual GIP and GLP-1 mechanism that affects how your body regulates appetite, blood sugar, and fat storage. This is an important distinction — the medication helps you eat less and feel fuller, rather than burning more calories at rest. Understanding exactly how Mounjaro works can help you set realistic expectations if you're considering this prescription injection for weight management in the UK.
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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 Works
Mounjaro is a dual GIP and GLP-1 receptor agonist — meaning it activates two natural hormone pathways rather than one. Here's what happens in your body:
- GLP-1 activation: Signals to your brain that you're full, reducing appetite and food cravings
- GIP activation: Works alongside GLP-1 to support blood sugar control and may influence how your body uses and stores fat
- Slowed gastric emptying: Food moves more slowly through your stomach, so you feel satisfied longer after meals
- Reduced hunger hormones: The medication suppresses ghrelin (the hunger hormone) and increases satiety signals
This is different from simply "speeding up metabolism." Your resting metabolic rate (calories burned at rest) doesn't significantly increase. Instead, you naturally consume fewer calories because you're genuinely less hungry. Try our GLP-1 weight loss calculator to explore how different Mounjaro doses might support weight loss when combined with reduced-calorie eating and 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.
UK Cost, Access, and How to Get Mounjaro
In the UK, Mounjaro is available through two routes. NHS access is through specialist tier 3 weight management services following a GP referral, though waiting lists and availability vary significantly by region and integrated care board (ICB). Private prescription is available through GPhC-registered online services after a clinical assessment with a UK-licensed prescriber — this typically costs between £129–£320 per month depending on your starting dose (2.5 mg) and current dose (up to 15 mg). Each KwikPen contains four weekly injections. Private access is faster but requires payment. Your GP can advise which route suits your circumstances. Use our BMI calculator to check if you meet typical eligibility thresholds (BMI 30+, or 27+ with weight-related health conditions).
- 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 increase your metabolic rate?
Not directly. Mounjaro doesn't significantly increase your resting metabolic rate. Instead, it reduces appetite and helps you feel fuller on smaller portions, creating a natural calorie deficit. Weight loss results from eating less, not burning more at rest.
How much weight can you lose with Mounjaro in the UK?
Clinical trials showed average weight loss of 15–21% of body weight over 72 weeks, alongside a reduced-calorie diet and increased physical activity. Individual results vary significantly — some people lose more, some less. Your GP or prescriber can discuss realistic expectations for you.
Is Mounjaro available on the NHS in the UK?
Yes, Mounjaro (tirzepatide) is approved by NICE for NHS use through specialist weight management services. However, access varies by region and waiting times can be lengthy. Private prescription options are available faster but involve out-of-pocket costs.
What's the difference between Mounjaro and Wegovy for weight loss?
Both are prescription weight loss injections. Mounjaro is a dual GIP+GLP-1 agonist; Wegovy is GLP-1 only. Mounjaro showed slightly higher average weight loss in trials (~20.9% vs ~15%), but both require clinical assessment, lifestyle changes, and individual results vary considerably.
How long does Mounjaro take to work?
Most people notice reduced appetite within the first 1–2 weeks of starting Mounjaro. Measurable weight loss typically appears after 4–6 weeks. Full effects emerge as your dose increases over 16–20 weeks. Your prescriber will review progress and adjust your dose as needed.
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.