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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What's the Difference Between Wegovy and Mounjaro in the UK?
Wegovy and Mounjaro are both prescription-only weight management injections available in the UK, but they work differently and have different costs and access routes. Wegovy (semaglutide) is a GLP-1 receptor agonist, while Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — meaning Mounjaro activates two hormone pathways instead of one. Both are once-weekly injections, both require clinical assessment, and both can be accessed through NHS specialist services or private prescription. This guide explains the key differences, costs, and how to access each in the UK.
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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.
Medication Differences and Expected Weight Loss
Wegovy (semaglutide) activates only the GLP-1 hormone pathway, which helps regulate appetite and slow how quickly food leaves the stomach. In clinical trials (STEP-1), participants taking Wegovy lost an average of approximately 14.9% of their body weight over 68 weeks at the maximum dose of 2.4 mg.
Mounjaro (tirzepatide) activates both GIP and GLP-1 pathways, which is why some people experience stronger appetite suppression. In the SURMOUNT-1 clinical trial, participants on the maximum 15 mg Mounjaro dose lost an average of approximately 20.9% of body weight — slightly more than Wegovy trial participants on average, though individual results vary significantly.
- Wegovy: starts at 0.25 mg, increases to maximum 2.4 mg over 16 weeks
- Mounjaro: starts at 2.5 mg, increases to maximum 15 mg over 20 weeks
- Both require a reduced-calorie diet and increased physical activity for best results
- Both are administered once weekly as pre-filled injection pens
Neither medication assures weight loss — results depend on individual factors, adherence, and lifestyle changes. Use our free GLP-1 weight loss calculator to estimate potential results at different dose levels.
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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.
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UK Cost and Access — NHS vs Private Routes
NHS access: Both Wegovy and Mounjaro are available through NHS specialist tier 3 and tier 4 weight management services, but only if referred by your GP. Waiting times vary significantly by region (integrated care board), and many areas have substantial waiting lists. NHS access is free at the point of use but availability is limited and regional.
Private access: Both medications are available through private online prescription services following an online clinical assessment with a UK-licensed prescriber. Costs vary by dose and provider, typically ranging from £129–£320 per month depending on whether you're at a starting dose or maximum dose. A Mounjaro KwikPen (4 weeks supply) costs more at higher doses than Wegovy at equivalent weight loss stages, but Mounjaro typically reaches maximum dose (15 mg) in fewer weeks than Wegovy reaches 2.4 mg. Private prescriptions are dispensed by GPhC-registered pharmacies and do not require NHS referral.
- 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 more effective than Wegovy?
In clinical trials, Mounjaro (tirzepatide) showed slightly higher average weight loss (approximately 21% vs 15% for Wegovy) due to its dual GIP and GLP-1 mechanism. However, individual results vary greatly and depend on genetics, lifestyle, and adherence. Both are effective for many people — the "better" option depends on your personal response and medical history, assessed by your prescriber.
Which is cheaper — Wegovy or Mounjaro?
At starting doses, Wegovy may cost slightly less. However, Mounjaro reaches its maximum effective dose (15 mg) in 20 weeks, while Wegovy reaches maximum (2.4 mg) in 16 weeks. At equivalent weight loss stages, costs are often comparable. Private prices vary by provider, so comparing quotes is recommended before committing.
Can I switch from Mounjaro to Wegovy or vice versa?
Switching between medications is possible but must be managed by your prescriber. There is no official conversion chart — approximate equivalences exist (for example, Mounjaro 10 mg is roughly equivalent to Wegovy 1.7 mg) but switching requires individual assessment. Never attempt to switch without medical guidance.
How do I access Mounjaro on the NHS?
Ask your GP for a referral to your local tier 3 specialist weight management service. You'll need a BMI of 30 or above (or 27+ with weight-related health conditions like type 2 diabetes or high blood pressure). Assessment and prescription happen through the specialist service. Waiting times vary significantly by region.
Can I get either medication through a private online prescription?
Yes, both Wegovy and Mounjaro are available through private UK online prescribing services. You complete a clinical assessment with a UK-licensed prescriber, and if approved, a prescription is issued and dispensed by a GPhC-registered pharmacy. No NHS referral is needed. This route is typically faster than NHS access but you pay privately.
Ready to take control of your weight loss journey?
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