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 Increase Metabolism?
Mounjaro (tirzepatide) doesn't directly increase your metabolism in the traditional sense. Instead, it works through a different mechanism: it reduces your appetite and helps you feel fuller after eating less food. This means you consume fewer calories, which creates the calorie deficit needed for weight loss. Clinical trials showed that people using Mounjaro lose weight because they eat less, not because their body burns calories faster. Understanding how Mounjaro actually works — rather than expecting a metabolic boost — helps set realistic expectations for your weight loss journey.
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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 Works in Your Body
Mounjaro is a dual GIP and GLP-1 receptor agonist, which means it activates two separate hormone pathways in your body. These natural hormones regulate appetite and energy use.
- GLP-1 activation: Signals to your brain that you're full, reducing hunger and food cravings
- GIP activation: Helps regulate how your body uses glucose and fat
- Gastric emptying: Slows how quickly food leaves your stomach, which extends feelings of fullness
The result is that you naturally eat less without feeling deprived. This calorie reduction — not a faster metabolism — is what drives weight loss on Mounjaro. Each Mounjaro KwikPen dose is injected once weekly, and the dose titration schedule starts at 2.5mg and increases gradually to find your optimal dose. In the SURMOUNT clinical trials, participants achieved average weight loss of 15–21% of their body weight over 72 weeks, all whilst following a reduced-calorie diet and increasing 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.
Metabolism vs Appetite — What's the Difference?
Many people assume weight loss injections "speed up" metabolism, but appetite suppression is actually more powerful. Your metabolic rate — the calories your body burns at rest — changes very little with Mounjaro. What changes dramatically is how much you eat.
Think of it this way: if you normally eat 2,500 calories and feel satisfied, but Mounjaro helps you feel full on 2,000 calories, you've created a 500-calorie daily deficit without your body burning any faster. That deficit leads to approximately 0.5kg weight loss per week — the NHS-recommended safe rate. For eligibility on the NHS or through private prescribing, you'll need a BMI of 30 or above, or 27 or above with weight-related health conditions like type 2 diabetes or high blood pressure. If you're unsure about your eligibility, use our free BMI calculator above to check your personal BMI, and discuss Mounjaro vs Wegovy options with your GP or a licensed prescriber.
- 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 speed up your metabolism?
No, Mounjaro doesn't increase your metabolic rate. Instead, it reduces appetite and helps you eat less. Weight loss happens because you consume fewer calories, not because your body burns calories faster. This appetite suppression is more effective for weight loss than trying to boost metabolism alone.
Will I still lose weight if my metabolism is slow?
Yes. Mounjaro works by reducing appetite, which is independent of your metabolic rate. Even with a slower metabolism, eating fewer calories creates the deficit needed for weight loss. Your GP can assess whether Mounjaro is appropriate for your individual circumstances.
What's the difference between Mounjaro and Wegovy for metabolism?
Both work primarily through appetite suppression, not metabolic acceleration. Mounjaro uses dual GIP and GLP-1 activation, while Wegovy (semaglutide) uses GLP-1 only. Neither directly increases metabolism — both create weight loss by helping you eat less alongside dietary changes.
How much weight can I expect to lose with Mounjaro?
Clinical trials showed average weight loss of 15–21% of body weight over 72 weeks alongside reduced-calorie diet and increased activity. Results vary significantly between individuals. Try our GLP-1 weight loss calculator above to estimate potential results at different doses based on your current weight.
Is Mounjaro available on the NHS in the UK?
Yes, Mounjaro (tirzepatide) is NICE-approved for NHS use through specialist tier 3 weight management services. However, regional availability varies and waiting lists can be long. Private prescribing is also available following an online clinical assessment through registered UK pharmacies.
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.