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: Medical Comparison
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight management injections licensed in the UK, but they work differently and have distinct clinical profiles. This guide compares the medical evidence, mechanism of action, dosing schedules, and trial outcomes to help you understand the key differences. Your prescriber will assess which is more suitable based on your individual health circumstances. Use our free GLP-1 weight loss calculator to estimate potential outcomes with either medication.
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Calculate Your BMI Instantly
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 Work Differently
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two separate hormone pathways in the body. This dual mechanism may help suppress appetite more effectively and supports feeling fuller after smaller meals. Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating a single pathway. Both slow gastric emptying (how quickly food leaves the stomach), but Mounjaro's dual action is why some clinical evidence shows slightly higher average weight loss. However, this does not mean Mounjaro is "better" — individual responses vary significantly, and some patients respond excellently to Wegovy alone. The choice depends on your personal health profile, medical history, and prescriber assessment.
- Mounjaro: GIP + GLP-1 dual mechanism
- Wegovy: GLP-1 single mechanism
- Both: once-weekly injections
- Both: require prescription and clinical assessment
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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.
Clinical Trial Data and Weight Loss Outcomes
In the SURMOUNT-1 trial, Mounjaro 15 mg helped participants lose an average of approximately 20.9% of their body weight over 72 weeks alongside reduced-calorie diet and exercise. In the STEP-1 trial, Wegovy 2.4 mg (the maximum dose) showed average weight loss of approximately 14.9% over 68 weeks under similar conditions. These figures represent clinical trial averages — individual results vary considerably, and some patients on Wegovy achieve similar percentage losses to Mounjaro, whilst others may require dose adjustments. Both medications work best when combined with dietary changes and increased physical activity. Your GP or prescriber can help you understand realistic expectations based on your personal circumstances.
- 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 is the main difference between Mounjaro and Wegovy?
Mounjaro is a dual GIP and GLP-1 receptor agonist, whilst Wegovy is a GLP-1 receptor agonist only. This means Mounjaro activates two hormone pathways, whilst Wegovy activates one. Both are once-weekly injections licensed for weight management in the UK, but they have different dosing schedules and clinical trial profiles.
Which medication causes more weight loss — Mounjaro or Wegovy?
Clinical trials show Mounjaro 15 mg achieved approximately 20.9% average weight loss, whilst Wegovy 2.4 mg achieved approximately 14.9%. However, individual results vary significantly. Some people respond better to one medication than the other. Your prescriber will assess which is more suitable for you personally.
How many injections does each medication require per week?
Both Mounjaro and Wegovy are once-weekly injections. You inject once per week, on the same day each week. Each pre-filled pen contains four weeks of doses. Mounjaro starts at 2.5 mg, whilst Wegovy starts at 0.25 mg, with different escalation schedules.
Are Mounjaro and Wegovy available on the NHS in the UK?
Both medications are NHS-approved and available through specialist tier 3 weight management services following GP referral. However, NHS availability varies by region and waiting lists can be long. Both are also available privately through GPhC-registered pharmacies following an online clinical assessment with a UK-licensed prescriber.
Can you switch from Mounjaro to Wegovy or vice versa?
It is possible to switch between medications, but this must be managed by your prescriber. There is no official established conversion chart between the two. Any switch requires a clinical assessment, and there may be a washout period between stopping one and starting the other.
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.