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 Affect Metabolism?
Mounjaro (tirzepatide) does affect how your body processes food and energy, though not directly in the way you might expect. Rather than permanently "boosting" metabolism, Mounjaro works by reducing appetite and helping you eat less — which indirectly affects how your body uses energy. This prescription-only injection activates two hormone pathways (GIP and GLP-1) that influence hunger signals, food absorption, and how quickly your stomach empties. Understanding this distinction helps set realistic expectations about how the medication supports weight management alongside a reduced-calorie diet and increased physical activity.
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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 Metabolism and Energy Use
Mounjaro doesn't work by speeding up your resting metabolic rate — the calories your body burns at rest. Instead, it affects how much you eat, which indirectly influences overall energy balance. The medication activates GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) receptors in the brain and gut, signalling fullness, reducing cravings, and slowing gastric emptying (how quickly food moves through your stomach). This means you feel satisfied with smaller portions and are less likely to snack between meals.
A secondary effect is improved glucose metabolism. Mounjaro helps your body manage blood sugar more effectively, which may reduce energy crashes and cravings that trigger overeating. However, this is different from a permanent increase in metabolic rate. The calorie deficit created by eating less — combined with physical activity — drives weight loss, not a change in how many calories your body "burns" at rest.
- Reduces appetite through hormone signalling
- Slows stomach emptying, increasing fullness
- Improves blood sugar control
- Decreases food cravings between meals
- Does not permanently increase resting metabolic rate
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.
What Happens to Your Metabolism When You Stop Mounjaro?
When you stop taking Mounjaro, your metabolic rate returns to its baseline — it doesn't drop or become "slower" because the medication doesn't permanently alter how your body burns calories. However, appetite typically returns to pre-treatment levels within weeks. This is why sustainable weight management after Mounjaro involves maintaining the lifestyle changes (healthier diet, increased physical activity, behaviour shifts) that were developed during treatment. Many people find that the habits and awareness built while taking Mounjaro help them keep weight off long-term, even after stopping the medication. Your GP or prescriber can discuss long-term weight management strategies with you.
- 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 permanently?
No. Mounjaro doesn't permanently increase your resting metabolic rate. It reduces appetite and helps you eat less, which creates a calorie deficit. Weight loss results from eating fewer calories, not from faster metabolism. Once you stop Mounjaro, your metabolic rate returns to baseline, though appetite changes also reverse.
Will my metabolism slow down when I stop taking Mounjaro?
Your metabolism won't slow down below your natural baseline. However, appetite typically returns to pre-treatment levels, making it easier to regain weight without the lifestyle habits built during treatment. This is why sustainable diet and exercise changes are important for maintaining results long-term.
How does Mounjaro affect blood sugar and energy metabolism?
Mounjaro improves how your body manages blood sugar by enhancing insulin response and reducing glucose spikes. This can stabilise energy levels and reduce cravings. However, this is glucose metabolism support, not a general "metabolic boost." Better blood sugar control helps you feel more stable and less likely to overeat.
Can I use our GLP-1 weight loss calculator to estimate results with Mounjaro?
Yes. MyWeightCheck's GLP-1 weight loss calculator can help you explore projected weight loss outcomes at different Mounjaro doses based on clinical trial data. Remember that individual results vary significantly — your actual weight loss will depend on your diet, activity level, starting weight, and personal metabolism.
Is Mounjaro the same as other weight loss injections like Wegovy?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight loss injections, but they work differently. Mounjaro is a dual GIP and GLP-1 agonist, while Wegovy activates GLP-1 only. Clinical trials suggest Mounjaro may support slightly greater average weight loss, though individual results vary. Your prescriber will advise which is suitable for you.
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.