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
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Does Mounjaro Affect Metabolism? Mounjaro vs Wegovy Explained
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) affect how your body regulates appetite and energy use, but they work slightly differently. Mounjaro is a dual GIP and GLP-1 receptor agonist, while Wegovy is a GLP-1 agonist only. Understanding these differences can help you and your GP discuss which prescription medication might be more suitable for your individual health needs. Neither medication directly "speeds up" metabolism in the traditional sense, but both influence the hormonal systems that regulate hunger, fullness, and how your body uses nutrients.
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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 Affect Metabolism: The Science
Mounjaro's dual mechanism: Mounjaro activates two hormone pathways—GIP (glucose-dependent insulinotropic polypeptide) and GLP-1. This dual action may help regulate appetite more effectively than GLP-1 alone. Clinical trials (SURMOUNT-1) showed Mounjaro helped participants lose an average of 15–21% body weight at maximum dose over 72 weeks, though individual results vary significantly.
Wegovy's single mechanism: Wegovy targets only the GLP-1 pathway. The STEP-1 trial showed average weight loss of approximately 15% body weight at 68 weeks on the maximum 2.4mg dose, alongside reduced-calorie diet and increased physical activity.
Neither medication directly increases metabolic rate. Instead, they work by slowing gastric emptying (how quickly food leaves your stomach), signalling fullness to your brain, and reducing food cravings. This helps you consume fewer calories naturally. Both require a UK prescription and clinical assessment from a licensed prescriber or GP before starting.
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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.
Which Is Right for You? Individual Suitability and Assessment
Choosing between Mounjaro and Wegovy depends on your personal health profile, medical history, and how your body responds to treatment. Both are prescription-only medications available through NHS specialist weight management services or private prescribing pathways in the UK. Your prescriber will assess factors including your BMI, any weight-related health conditions, current medications, and contraindications.
Clinical trial data shows both medications support meaningful weight loss, but there is no universal "best" choice—outcomes vary by individual. Some people respond better to the dual GIP+GLP-1 approach of Mounjaro; others achieve their goals with Wegovy's GLP-1 mechanism alone. Always discuss your eligibility, potential side effects, and realistic expectations with your GP or a licensed prescriber before starting treatment. Use our free GLP-1 weight loss calculator to estimate potential weight loss projections at different doses, and our BMI calculator to establish your starting point.
- 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 does not directly increase metabolic rate. Instead, it works by reducing appetite, helping you feel fuller after smaller meals, and slowing stomach emptying. Weight loss then occurs because you consume fewer calories overall, not because your metabolism is faster. Individual results vary.
Is Mounjaro better than Wegovy for metabolism?
Both medications affect metabolic regulation differently. Mounjaro uses a dual GIP+GLP-1 mechanism; Wegovy uses GLP-1 only. Clinical trials show both support weight loss—Mounjaro averaged 15–21%, Wegovy around 15%. Neither is universally "better"; suitability depends on your individual health profile and prescriber assessment.
How does the GIP mechanism in Mounjaro work differently?
GIP (glucose-dependent insulinotropic polypeptide) is a second hormone pathway that Mounjaro activates alongside GLP-1. This dual action may provide additional appetite regulation compared to GLP-1 alone. However, long-term comparative outcomes between dual and single mechanisms are still emerging in clinical practice.
Can I switch from Wegovy to Mounjaro if metabolism slows?
Any switch between prescription medications must be managed by your prescriber. They will assess whether a change is appropriate based on your response, side effects, and health status. Do not stop or switch medications without medical guidance. Contact your GP or prescriber to discuss concerns.
Will my metabolism return to normal after stopping Mounjaro?
Yes. Metabolic effects from Mounjaro are reversible. Once you stop the injection, appetite-regulating hormones return to baseline within days to weeks. Weight regain is possible without sustained dietary and lifestyle changes. Your prescriber can discuss long-term management strategies with 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.