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 — What NHS Guidelines Say
If you're considering weight loss medication through the NHS, you may have heard about both Mounjaro (tirzepatide) and Wegovy (semaglutide). Both are prescription-only GLP-1-based medications approved for weight management in UK adults, but they work slightly differently and have different clinical evidence. Understanding the differences helps you and your GP make an informed decision about which may be more suitable for your individual circumstances. This guide explains the key differences between Mounjaro and Wegovy under NHS guidelines.
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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 Differ — Clinical Evidence
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways. Clinical trial data from the SURMOUNT-1 study showed that participants taking Mounjaro at the maximum 15 mg dose achieved an average weight loss of approximately 20.9% of body weight over 72 weeks, alongside a reduced-calorie diet and increased physical activity.
Wegovy (semaglutide) is a single GLP-1 receptor agonist. The STEP-1 clinical trial showed that participants on the maximum 2.4 mg dose achieved an average weight loss of approximately 14.9% of body weight over 68 weeks, also with lifestyle changes. Individual results vary significantly — not everyone loses the same amount.
- Mounjaro dosing: 2.5 mg up to 15 mg once weekly
- Wegovy dosing: 0.25 mg up to 2.4 mg once weekly
- Both are once-weekly injections (the Mounjaro KwikPen device or Wegovy auto-injection pen)
- Both require a clinical assessment before prescription
The dual mechanism of Mounjaro may provide different effects compared to Wegovy's single GLP-1 pathway, but both have been shown to support weight loss when used with lifestyle changes.
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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.
NHS Eligibility and Prescriber Decision
Under current NHS guidelines, you may be eligible for either Mounjaro or Wegovy if you have a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds (27.5 or above) apply.
The choice between Mounjaro and Wegovy is not based on which is "better" — it is a clinical decision made by your prescriber based on your health history, medical conditions, and individual circumstances. Your GP or specialist will assess which medication profile suits you best. Both are prescription-only and require ongoing medical supervision. Use our free BMI calculator to check your personal eligibility threshold, and discuss both options with your healthcare provider to understand which approach aligns with your health needs.
- 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 key difference between Mounjaro and Wegovy?
Mounjaro is a dual GIP and GLP-1 receptor agonist (activates two hormone pathways), while Wegovy is a single GLP-1 agonist. This different mechanism may produce different effects on appetite and weight loss, but both require lifestyle changes for best results.
Which one will the NHS prescribe — Mounjaro or Wegovy?
The NHS doesn't automatically choose one over the other. Your GP or specialist prescriber will assess your health history and decide which is more appropriate for you clinically. Both are available through NHS specialist weight management services where there is capacity.
What does the clinical trial data show about weight loss?
SURMOUNT-1 trial data showed Mounjaro participants lost approximately 20.9% body weight on 15 mg. STEP-1 trial data showed Wegovy participants lost approximately 14.9% on 2.4 mg. However, individual results vary significantly, and both results were achieved alongside diet and exercise changes.
Are both available on the NHS?
Yes, both Mounjaro and Wegovy are available through NHS specialist tier 3 weight management services, though regional availability varies. Waiting times can be substantial in many areas. Private prescription routes are also available through UK-licensed prescribers.
Do I need a prescription for either medication?
Yes, both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only medicines in the UK. You cannot buy them over the counter. A licensed prescriber must assess your suitability before issuing a prescription, whether through the NHS or private routes.
Ready to take control of your weight loss journey?
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