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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Wegovy vs Mounjaro in the UK: What's the Difference?
Both Wegovy (semaglutide) and Mounjaro (tirzepatide) are prescription-only weight loss injections licensed in the UK, but they work differently and have different access routes through the NHS and private prescribing. This guide explains the key differences, eligibility criteria, and how to access each one, so you can understand your options if your GP refers you to specialist weight management services or you're considering private prescription weight loss treatment.
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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 Wegovy and Mounjaro Differ: Mechanism and Doses
Wegovy (semaglutide) is a GLP-1 receptor agonist — it activates one natural hormone pathway that signals fullness and reduces appetite. In clinical trials (STEP-1), participants lost an average of around 15% of their body weight over 68 weeks at the maximum 2.4 mg dose.
Mounjaro (tirzepatide) uses a dual mechanism — it's a GIP and GLP-1 receptor agonist, activating two hormone pathways. Clinical trial data (SURMOUNT-1) showed average weight loss of approximately 20.9% at the maximum 15 mg dose over 72 weeks.
- Wegovy: once-weekly 0.25 mg to 2.4 mg injection
- Mounjaro: once-weekly 2.5 mg to 15 mg injection (or kwikpen device)
- Both are weight loss injections, not insulin
- Individual results vary significantly — clinical trial averages do not predict personal outcomes
- Both require a reduced-calorie diet and increased physical activity alongside medication
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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 vs Private Prescribing in the UK
Through the NHS, both Wegovy and Mounjaro are available via tier 3 specialist weight management services — your GP can refer you if you meet eligibility criteria (BMI ≥30, or ≥27 with weight-related health conditions). However, NHS availability varies significantly by region and waiting lists can be lengthy.
Privately, both are available through GPhC-registered online prescribers without an NHS referral. A licensed prescriber assesses you via online consultation, issues a prescription if appropriate, and a pharmacy dispenses the medication. Use our free GLP-1 weight loss calculator to estimate potential results at different doses, and our BMI calculator to check where you currently sit on the NHS eligibility scale. Costs typically range from £129–£320 per month depending on dose and provider.
- 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.
Which weight loss injection works better — Wegovy or Mounjaro?
Clinical trials suggest Mounjaro may produce slightly higher average weight loss (around 21% vs 15%), but individual results vary greatly. Neither is "better" — suitability depends on your health profile, how you respond, and what your prescriber recommends. Always discuss both options with a healthcare professional.
Can I switch from Wegovy to Mounjaro on the NHS?
Potentially, yes — if you're in an NHS specialist weight management service and your prescriber feels a switch is clinically appropriate. There is no official NHS conversion chart, so your prescriber will assess your individual response. Any medication switch must be managed by your healthcare provider, not self-initiated.
What's the cost difference between Wegovy and Mounjaro privately in the UK?
Costs vary by dose and provider, but both typically range from £129–£320 per month. Starting doses are cheaper; maximum doses are most expensive. Get quotes from GPhC-registered pharmacies to compare. NHS access is free through specialist services, though waiting times can be significant.
Do I need a referral to a GP to get Wegovy or Mounjaro privately in the UK?
No — for private prescribing, you can consult a UK-licensed prescriber directly through an online platform without a GP referral. For NHS access, your GP must refer you to a tier 3 specialist weight management service. Private access is faster but involves upfront cost.
Are Wegovy and Mounjaro the same as Ozempic?
No — Ozempic also contains semaglutide but is licensed for type 2 diabetes (maximum 2 mg dose), not weight management. Wegovy is the licensed weight loss version of semaglutide (up to 2.4 mg). Mounjaro is a different medication entirely (tirzepatide). Using Ozempic for weight loss is off-label and not recommended. ```
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