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?
Both Wegovy and Mounjaro are prescription-only weight management injections licensed in the UK, but they work in different ways and show different results in clinical trials. Understanding how they differ can help you discuss options with your GP or prescriber. This guide compares the two medications factually — which one may be suitable depends entirely on your individual health, medical history, and prescriber assessment.
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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 Differently
Wegovy (semaglutide) is a GLP-1 receptor agonist — it activates a single hormone pathway to reduce appetite and help you feel fuller after eating. Mounjaro (tirzepatide) is different: it's a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways at once. This dual mechanism is what sets Mounjaro apart. In clinical trials, the STEP trial showed Wegovy helped participants lose an average of approximately 15% of body weight over 68 weeks. The SURMOUNT trial data for Mounjaro showed average weight loss ranging from 15–21% depending on dose, with the highest dose (15 mg) producing approximately 21% average weight loss. Individual results vary significantly. Both medications are injected once weekly and require dose titration starting from a low dose and gradually increasing over several weeks.
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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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Comparing Doses, Costs, and Prescriber Choice
Wegovy starts at 0.25 mg and reaches a maximum of 2.4 mg per week. Mounjaro begins at 2.5 mg and reaches 15 mg per week. Because Mounjaro has a dual mechanism, lower mg amounts don't directly compare to Wegovy — a Mounjaro KwikPen at 10 mg is not directly equivalent to Wegovy at a certain dose. Your prescriber will assess your individual health, medical history, and response to decide which medication (if either) is appropriate for you. Both are prescription-only and require clinical assessment. Access in the UK is through NHS specialist weight management services (often with long waiting lists) or private online prescribing following an online clinical 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.
Is Mounjaro better than Wegovy?
Clinical trial data shows Mounjaro may produce slightly higher average weight loss than Wegovy, but "better" depends on individual factors. Some people respond better to one medication than another. Your prescriber will assess which is more suitable for you based on your health, medical history, and any other medications you take. Both are effective prescription-only treatments.
Why does Mounjaro have higher dose numbers than Wegovy?
Mounjaro (tirzepatide) and Wegovy (semaglutide) are different medications with different mechanisms and formulations. Mounjaro's dual GIP and GLP-1 action means its dosing scale isn't directly comparable to Wegovy's single GLP-1 mechanism. Dose numbers reflect how each medication is dosed, not strength differences.
Can you switch from Wegovy to Mounjaro or vice versa?
Switching between medications must only be done under prescriber supervision. There is no official established conversion chart between Wegovy and Mounjaro doses. If you're considering a switch, discuss this with your GP or prescriber — they'll assess whether it's appropriate and how to manage the transition safely.
Which has fewer side effects — Wegovy or Mounjaro?
Both medications have similar side effects (nausea, diarrhoea, constipation, stomach pain). Side effect severity varies between individuals and often improves as your body adjusts. Your prescriber will discuss potential side effects and how to manage them. Neither medication is side-effect-free.
How do I know which medication is right for me?
This is entirely an individual decision made with your prescriber. They'll assess your BMI, medical history, any weight-related health conditions, other medications you take, and your personal preference. Use our free GLP-1 weight loss calculator and BMI calculator to gather your health information before your consultation, but only a qualified prescriber can recommend which medication suits you.
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.