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: Complete Comparison Chart
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight loss injections licensed in the UK, but they work differently and may suit different people. This guide compares the two medicines side-by-side using clinical trial data and NHS guidance, helping you understand the key differences. Whether you're considering one or the other, your GP or a UK-licensed prescriber will assess which is appropriate for your individual health needs. Use our free BMI calculator and GLP-1 weight loss calculator to explore your eligibility and potential outcomes.
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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: Mechanism Differences
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist. It activates two hormone pathways at once: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1). This dual action may help regulate appetite, reduce cravings, and support feeling fuller after meals.
Wegovy (semaglutide) is a GLP-1 receptor agonist only. It targets the single GLP-1 pathway, which signals satiety to the brain and slows gastric emptying. Both mechanisms support appetite reduction and modest weight loss.
In simple terms: Mounjaro uses two pathways; Wegovy uses one. This is why Mounjaro showed slightly higher average weight loss in clinical trials, though individual results vary significantly and prescriber choice depends on your personal health profile, not just mechanism.
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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.
Dose Chart and Clinical Trial Outcomes
Mounjaro (SURMOUNT-1 trial): Starting dose 2.5 mg, escalating weekly up to 15 mg maximum. Average weight loss at 72 weeks: 15–21% of body weight (depending on final dose). Alongside reduced-calorie diet and increased physical activity.
Wegovy (STEP-1 trial): Starting dose 0.25 mg, escalating weekly up to 2.4 mg maximum. Average weight loss at 68 weeks: approximately 14.9% of body weight. Also used with dietary and activity changes.
Both are once-weekly injections. Neither is a structured approach—results depend on adherence, lifestyle, and individual response. Your prescriber will use a Mounjaro KwikPen or Wegovy auto-injection pen based on what suits you best. Track your progress using our free progress tracker.
- 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 more effective than Wegovy?
Clinical trials showed Mounjaro achieved slightly higher average weight loss (15–21%) compared to Wegovy (14.9%), but individual results vary significantly. Both are effective; suitability depends on your health profile, other medications, and prescriber assessment. There is no one-size-fits-all answer.
What is the main difference between Mounjaro and Wegovy?
Mounjaro is a dual GIP+GLP-1 agonist (two hormone pathways), while Wegovy is a GLP-1 agonist only (one pathway). Mounjaro uses the dual mechanism as its key difference. Both require prescription and clinical assessment in the UK.
Can I switch from Mounjaro to Wegovy or vice versa?
Switching between medicines is possible but must be managed by your prescriber. Approximate dose equivalence exists (e.g., Mounjaro 10 mg ≈ Wegovy 1.7 mg), but any switch requires stopping one and starting the other under medical guidance. Never attempt to switch without prescriber instruction.
Which is easier to use—Mounjaro KwikPen or Wegovy pen?
Both are pre-filled, once-weekly auto-injection pens designed for ease of use. Mounjaro contains 4 doses per KwikPen; Wegovy uses individual pens. Choice is often based on prescriber familiarity, availability, and your personal preference. Your prescriber will advise.
Are Mounjaro and Wegovy available on the NHS in the UK?
Both are NICE-approved and available through NHS specialist tier 3 weight management services, but availability and waiting times vary significantly by region. Private access is available through online UK prescribers. Always consult your GP or a prescriber about your options.
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.