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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Mounjaro vs Wegovy on the NHS: What's the Difference?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight loss injections available through the NHS and private prescribing in the UK. They work differently and have different trial outcomes, so understanding the distinction helps you discuss options with your GP. This guide compares the two side-by-side, covering how they work, expected weight loss, and NHS access routes—so you can make an informed decision about which might suit your circumstances.
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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 Work Differently
Wegovy (semaglutide) is a GLP-1 receptor agonist—it activates a single hormone pathway (GLP-1) to reduce appetite and slow stomach emptying. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways simultaneously. This dual mechanism is what sets them apart and may explain slightly different weight loss outcomes in clinical trials.
- Wegovy: Single GLP-1 pathway; once-weekly injection; maximum dose 2.4 mg
- Mounjaro: Dual GIP + GLP-1 pathways; once-weekly injection; maximum dose 15 mg
In the STEP-1 clinical trial, Wegovy at 2.4 mg produced average weight loss of around 14.9% of body weight over 68 weeks. In the SURMOUNT-1 trial, Mounjaro at 15 mg produced average weight loss of approximately 20.9% over 72 weeks. However, individual results vary significantly, and both medications work best alongside reduced-calorie diet and increased physical activity.
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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
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NHS Access and Suitability: Which is Right for You?
Both medications are available through NHS specialist tier 3 weight management services if you meet eligibility criteria (BMI ≥30, or ≥27 with weight-related health conditions). NHS availability varies by region and waiting lists can be lengthy. A prescriber will assess your individual health, medications, and circumstances to determine suitability—neither is automatically "better" than the other. Factors like your medical history, other medications, side effect tolerance, and injection preferences guide the decision. Use our free BMI calculator above to check your starting point, and speak with your GP about referral to specialist services or discuss private options if NHS waiting times are prohibitive.
- 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.
What is the main difference between Mounjaro and Wegovy?
Wegovy activates a single GLP-1 hormone pathway, while Mounjaro activates dual GIP and GLP-1 pathways. This dual mechanism in Mounjaro may contribute to slightly higher average weight loss in clinical trials, though individual responses vary significantly between people.
Which one causes more weight loss on the NHS?
On average, Mounjaro produced slightly higher weight loss in trials (20.9%) compared to Wegovy (14.9%), but these are averages. Your personal results depend on your metabolism, adherence, diet, and exercise—not just the medication itself. A prescriber will assess what suits you.
Can I get both Mounjaro and Wegovy on the NHS?
Both are available through NHS specialist weight management services if you meet eligibility criteria. However, NHS prescribing varies significantly by region (ICB). Waiting lists can be very long, and not all areas have equal access. Your GP can refer you to your local tier 3 service.
What are the main side effects of each?
Both share common side effects: nausea, diarrhoea, constipation, and stomach pain (especially early on). These often reduce over time. Mounjaro and Wegovy have similar safety profiles, though individual tolerance varies. Your prescriber will discuss side effect management.
How do I access Mounjaro or Wegovy if I'm not on the NHS waiting list?
Private prescribing is available through UK-licensed online prescribers following a clinical assessment. A GPhC-registered pharmacy then dispenses the prescription. Private costs vary by provider and dose but typically range from £130–£320 per month. NHS referral is not required for private access.
Ready to take control of your weight loss journey?
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