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 Versus Mounjaro in the UK — What's the Difference?
Both Wegovy (semaglutide) and Mounjaro (tirzepatide) are prescription-only weight loss injections approved in the UK, but they work differently and have distinct eligibility pathways. Understanding the key differences helps you and your GP decide which medication might be appropriate for you. Both are available through NHS specialist weight management services and private prescribing routes. This guide explains how they compare, what NHS guidance says, and how to access them 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.
How Wegovy and Mounjaro Work — The Key Difference
Mechanism of action is the fundamental difference between these medications. Wegovy (semaglutide) is a single GLP-1 receptor agonist — it activates one hormone pathway to reduce appetite and help you feel fuller after smaller meals. Mounjaro (tirzepatide), by contrast, is a dual GIP and GLP-1 receptor agonist — it activates two hormone pathways simultaneously, which may provide a stronger effect on appetite suppression.
In clinical trials, this difference showed measurable outcomes. The STEP-1 trial (Wegovy) showed average weight loss of approximately 14.9% of body weight at 68 weeks on the maximum 2.4 mg dose. The SURMOUNT-1 trial (Mounjaro) showed average weight loss of approximately 20.9% of body weight at 72 weeks on the maximum 15 mg dose. However, individual results vary significantly, and both medications must be used alongside a reduced-calorie diet and increased physical activity to be effective.
Both medications slow how quickly food leaves your stomach (gastric emptying), though this effect typically reduces over time with continued use.
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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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NHS Eligibility and Access in the UK
NHS eligibility criteria are the same for both Wegovy and Mounjaro. You may be eligible if you have a BMI of 30 kg/m² or above, or a BMI of 27–29.9 kg/m² 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 apply (27.5 and above may qualify).
Both medications are typically accessed through NHS tier 3 specialist weight management services, not standard GP prescription. Your GP would refer you to your local specialist service, where a multidisciplinary team assesses your eligibility. Regional variation is significant — some areas have shorter waiting lists than others. NICE has approved both medications for use within NHS services, but availability depends on your Integrated Care Board (ICB) commissioning decisions.
- 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's the main difference between how Wegovy and Mounjaro work?
Wegovy (semaglutide) is a single GLP-1 receptor agonist activating one appetite-control pathway. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist activating two pathways simultaneously. Clinical trials suggest Mounjaro may produce greater average weight loss, but individual results vary significantly.
Can I get Wegovy or Mounjaro through the NHS?
Yes, both are available through NHS tier 3 specialist weight management services following a clinical assessment. You'll need a GP referral to your local specialist service. Access depends on regional commissioning, and waiting lists vary significantly across the UK. Private online prescribing is also available without NHS referral.
Which medication is more effective for weight loss?
Clinical trials show Mounjaro achieved average weight loss of approximately 21% body weight, compared to Wegovy's approximately 15%. However, these are trial averages — individual responses vary considerably. Your prescriber will recommend the most suitable option based on your health profile and circumstances.
How do the dosing schedules differ between Wegovy and Mounjaro?
Wegovy starts at 0.25 mg weekly, escalating to a maximum of 2.4 mg weekly over 16 weeks. Mounjaro starts at 2.5 mg weekly, escalating to a maximum of 15 mg weekly over 20+ weeks. Both are once-weekly injections. Your prescriber determines the appropriate escalation schedule for you.
What happens if I want to switch from one medication to the other?
Switching between Wegovy and Mounjaro should only be managed by your prescriber. There is no official conversion chart between the medications. Your prescriber will assess whether switching is appropriate and will manage any transition carefully, as the two medications have different potencies and mechanisms. ```
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