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: Diet and Nutrition Support Comparison
If you're researching weight loss injections in the UK, you've likely encountered both Mounjaro and Wegovy. While both are prescription-only medications designed to support weight management, they work differently and may suit different individuals. This guide compares the two medications factually, looking at how they support dietary changes and what the clinical evidence shows. Your GP or prescriber will assess which is appropriate for you based on your individual health needs. Use our free GLP-1 weight loss calculator to explore potential outcomes with each medication type.
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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: Mechanism and Clinical Evidence
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways to regulate appetite and support feeling fuller after meals. Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating a single hormone pathway. In clinical trials, this difference shows in outcomes: the SURMOUNT-1 trial showed Mounjaro participants lost an average of 15–21% body weight at different doses over 72 weeks, whilst the STEP-1 trial showed Wegovy participants lost approximately 15% body weight on average at 68 weeks. Both results were achieved alongside a reduced-calorie diet and increased physical activity. Starting doses differ too: Mounjaro begins at 2.5 mg weekly and escalates to a maximum of 15 mg, whilst Wegovy starts at 0.25 mg and reaches 2.4 mg. Individual results vary significantly, and both require a clinical assessment before prescription.
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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.
Which Medication Suits Your Situation? Individual Suitability Factors
Neither Mounjaro nor Wegovy is universally "better"—suitability depends on your individual health profile, medical history, and how your body responds. Your prescriber will assess factors including your BMI, weight-related health conditions, other medications, and any contraindications. Both medications are UK prescription-only and available through NHS specialist weight management services or private online consultations. Both require ongoing clinical monitoring and support for lifestyle changes—medication works best alongside dietary changes and physical activity. Track your progress with our free progress tracker to monitor weight loss and other health improvements. The choice between them is individualised, and your GP or prescriber is best placed to guide you. Some people may respond better to one mechanism than the other, which is why honest discussion about your health history is essential during the assessment.
- 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.
Can I switch from Mounjaro to Wegovy if needed?
Yes, but any switch must be managed by your prescriber. There is no officially established conversion chart between the two medications. Your prescriber will assess whether a switch is appropriate and manage the transition safely. Stopping one and starting another requires careful clinical oversight, as the medications work via different mechanisms.
Do Mounjaro and Wegovy require the same diet changes?
Both work best alongside a reduced-calorie diet and increased physical activity. However, individual tolerance differs—some people experience nausea or appetite reduction that naturally supports eating smaller portions, whilst others need more active dietary planning. Your prescriber or a dietitian can advise on meal planning tailored to your situation.
Which medication is more effective for weight loss?
Clinical trials show both are effective. Mounjaro's SURMOUNT trial showed slightly higher average weight loss (up to 21%) compared to Wegovy's STEP trial (approximately 15%), but individual results vary widely. "More effective" depends on your personal response, not general averages. Your prescriber will discuss expected outcomes based on clinical evidence.
Are Mounjaro and Wegovy available on the NHS?
Yes, both are licensed in the UK for weight management and available through NHS specialist tier 3 weight management services following referral from your GP. Availability varies by region and waiting lists can be lengthy. Private prescriptions are also available through UK-licensed online services.
Do side effects differ between Mounjaro and Wegovy?
Both commonly cause nausea, diarrhoea, constipation, and stomach discomfort, particularly when starting or increasing doses. Mounjaro may cause additional side effects related to its dual mechanism. Individual experiences vary. Your prescriber will discuss potential side effects and how to manage them during your assessment.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.