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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Changing Your Mounjaro Supplier — Mounjaro vs Wegovy
If you're considering changing your Mounjaro supplier or exploring alternative weight loss injections like Wegovy, it helps to understand the key differences between the two treatments. Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight management injections licensed in the UK, but they work through different mechanisms and have different dose progressions. This guide compares the two side-by-side so you can make an informed discussion with your prescriber about what might suit your situation best.
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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 Dosing
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways in your body to help regulate appetite and support feeling fuller. It starts at 2.5mg and escalates over 20 weeks to a maximum of 15mg once weekly.
Wegovy (semaglutide) is a GLP-1 receptor agonist only — it activates a single hormone pathway. It starts at 0.25mg and escalates to a maximum of 2.4mg once weekly over 16 weeks.
In clinical trials, SURMOUNT (Mounjaro) showed average weight loss of approximately 15–21% of body weight depending on dose, while STEP (Wegovy) showed approximately 14.9% average weight loss. Individual results vary significantly. Both work best alongside a reduced-calorie diet and increased physical activity. Changing suppliers simply means switching from one prescriber or pharmacy to another — the medication itself remains the same.
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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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Which Medication Is Right for You — Individual Suitability
The choice between Mounjaro and Wegovy isn't about one being "better" — it's about which suits your individual health circumstances and how your body responds. Both require a prescription and a clinical assessment by a qualified prescriber. Your GP or specialist will consider your BMI, any weight-related health conditions (such as type 2 diabetes or high blood pressure), your medical history, and how you've responded to previous treatments. If you're already on Mounjaro and considering a switch, discuss this with your current prescriber — they may suggest continuing with Mounjaro, switching to Wegovy, or exploring other options. Our free BMI calculator and GLP-1 weight loss calculator can help you understand your eligibility and potential outcomes, but your prescriber's assessment is always the final decision.
- 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?
Yes. Switching between prescription weight loss medications requires guidance from your prescriber. Never stop one medication and start another without clinical advice. Your prescriber will assess whether Wegovy suits you better and manage any transition period safely. Always inform your new prescriber about your current Mounjaro doses and any side effects you've experienced.
What's the main difference between Mounjaro and Wegovy?
Mounjaro is a dual GIP and GLP-1 agonist (two hormone pathways), while Wegovy is a GLP-1 agonist only (one pathway). This dual mechanism may explain why Mounjaro showed slightly higher average weight loss in clinical trials, but individual responses vary. Both require prescription and clinical assessment.
Will changing suppliers affect my prescription?
Changing your supplier (GP, prescriber, or pharmacy) doesn't change the medication itself. However, you'll need a new prescription from your new prescriber. They'll review your medical history, current dose, and suitability before issuing a prescription. Some prescribers may recommend continuing at your current dose; others may restart the titration schedule.
What if I'm not happy with my current Mounjaro supplier?
If you're unhappy with your current supplier's service, communication, or cost, you can request a new prescription from another UK-licensed prescriber and use a different GPhC-registered pharmacy. You don't need a reason to change — prescribers in the UK can assess you independently. Always check your current contract terms before switching.
How do I know if I should switch to Wegovy instead of Mounjaro?
This is a conversation for your prescriber. Consider switching if: you're experiencing difficult side effects on Mounjaro, you've plateaued in weight loss, or your prescriber suggests Wegovy may be more suitable. Wegovy's once-weekly single injection and lower maximum dose may suit some people better. Use our GLP-1 weight loss calculator to compare projected outcomes at different doses.
Ready to take control of your weight loss journey?
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