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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Is Mounjaro Good for Weight Loss? What You Need to Know
Yes, Mounjaro (tirzepatide) is effective for weight loss in clinical trials, but whether it's "good" for you specifically depends on your individual health, prescriber assessment, and how your body responds. Both Mounjaro and Wegovy are prescription-only weekly weight loss injections licensed in the UK. They work differently and produce similar average results, though individual outcomes vary significantly. This guide compares the two medications to help you understand the evidence, not to recommend one over the other—your GP or prescriber makes that decision based on your personal health profile.
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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 and Wegovy Compare: Clinical Trial Evidence
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist—it activates two natural hormone pathways. In the SURMOUNT-1 clinical trial, participants on the maximum 15 mg dose lost an average of 20.9% of their body weight over 72 weeks alongside a reduced-calorie diet and increased physical activity.
Wegovy (semaglutide) is a GLP-1 receptor agonist only—it activates a single pathway. In the STEP-1 clinical trial, participants on the 2.4 mg dose lost an average of 14.9% of body weight over 68 weeks with the same lifestyle support.
- Mounjaro: up to 15 mg once weekly; average loss ~15–21% body weight
- Wegovy: up to 2.4 mg once weekly; average loss ~15% body weight
- Both: results vary; individual outcomes depend on dose, adherence, diet, and exercise
- Both: prescription-only; require clinical assessment before starting
The difference in trial results reflects Mounjaro's dual mechanism, though real-world outcomes depend on individual factors, not trial averages.
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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.
Who Should Use Which — and How Access Works in the UK
Both medications are prescribed based on individual clinical assessment, not personal preference. Your GP or prescriber will consider your BMI, any weight-related health conditions (like type 2 diabetes, high blood pressure, or sleep apnoea), how you've responded to other treatments, and any contraindications. You can use our free GLP-1 weight loss calculator to explore potential weight loss projections, but a prescriber must make the final decision.
Access in the UK: Mounjaro and Wegovy are available through NHS specialist weight management services (tier 3) or private online prescribing following a clinical assessment. NHS access involves referral from your GP and can involve waiting lists; private access is faster but at personal cost. Neither medication works without lifestyle changes—reduced calories and physical activity are essential for results.
- 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.
Is Mounjaro better than Wegovy for weight loss?
In clinical trials, Mounjaro produced slightly higher average weight loss (20.9% vs 14.9%) due to its dual mechanism. However, individual results vary significantly. "Better" depends on your personal response, health conditions, and which medication your prescriber deems suitable for you. Both are effective—the choice is clinical, not based on superiority.
How quickly will I lose weight on Mounjaro?
Weight loss varies widely. In trials, participants lost approximately 5–8% in the first 16 weeks, then continued losing over several months. The NHS recommends a sustainable rate of 0.5–1 kg per week. Some people respond faster; others lose less. Consistent diet and exercise are essential—the medication supports, not replaces, lifestyle change.
What's the difference between a GLP-1 and GIP/GLP-1 injection?
GLP-1 (Wegovy) activates one appetite-regulating hormone pathway. GIP/GLP-1 (Mounjaro) activates two pathways, which may explain slightly higher average weight loss in trials. Both slow stomach emptying and increase feelings of fullness. The dual action doesn't assures better results for everyone—prescriber assessment determines suitability.
Can I get Mounjaro on the NHS in the UK?
Yes—Mounjaro is NICE-approved for use in NHS specialist weight management services (tier 3). Access requires referral from your GP and varies significantly by region and waiting list availability. Many areas have lengthy waiting times. Private prescription through a UK-licensed prescriber is available as an alternative but involves personal cost.
Do I need to diet and exercise while taking Mounjaro or Wegovy?
Yes, absolutely. Both medications are approved for use alongside reduced-calorie diet and increased physical activity. Clinical trial weight loss was achieved with lifestyle changes—the injection alone is not sufficient. Your prescriber will discuss diet and exercise expectations before you start treatment.
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.