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
Free tracker included with every download this week
Mounjaro Vs Wegovy For Weight Loss
Both Mounjaro and Wegovy are prescription-only weight loss injections available in the UK, but they work differently and suit different people. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, while Wegovy (semaglutide) activates the GLP-1 pathway only. This guide compares their mechanisms, clinical trial results, doses, and side effects to help you understand the differences. Both require a clinical assessment and prescription from a UK-licensed prescriber — individual suitability is determined by your prescriber based on your health profile.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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 They Work — Mechanism and Clinical Trial Data
Mounjaro (tirzepatide) is a dual agonist, activating both GIP and GLP-1 receptors. This dual mechanism may explain its slightly higher average weight loss in clinical trials. In the SURMOUNT-1 trial, participants on 15 mg Mounjaro lost approximately 20.9% of their body weight over 72 weeks, alongside a reduced-calorie diet and increased physical activity. Wegovy (semaglutide) activates the GLP-1 pathway alone. In the STEP-1 trial, participants on 2.4 mg Wegovy lost approximately 14.9% of body weight at 68 weeks under the same lifestyle conditions.
- Average weight loss (Mounjaro 15 mg): ~20.9% body weight (SURMOUNT-1)
- Average weight loss (Wegovy 2.4 mg): ~14.9% body weight (STEP-1)
- Important: These are clinical trial averages — individual results vary significantly, and trials used different durations and populations
Both are weekly weight loss injections licensed for UK prescription use. Choosing between them depends on your prescriber's assessment and what they judge most suitable for your specific health needs.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
Doses, Side Effects, and Practical Differences
Mounjaro starts at 2.5 mg and increases weekly to a maximum of 15 mg, with a minimum 4-week interval between dose increases. Wegovy starts at 0.25 mg and increases over 16 weeks to a maximum 2.4 mg. Both commonly cause nausea, diarrhoea, constipation, and stomach pain, especially at higher doses, though side effects often improve over time. Neither is suitable during pregnancy or breastfeeding, and both are prescription-only medicines requiring clinical assessment. Access in the UK is through NHS specialist tier 3 weight management services or private online prescribing following consultation with a licensed prescriber. Your GP or prescriber can assess which medicine is most appropriate based on your individual health, preferences, and medical history.
- 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 show Mounjaro achieved slightly higher average weight loss (~20.9%) compared to Wegovy (~14.9%), but trials used different durations and populations. Individual results vary significantly. Effectiveness depends on how you respond to the medication and how well you maintain lifestyle changes. Your prescriber will choose based on what's most suitable for your health profile.
What's the main difference between Mounjaro and Wegovy mechanisms?
Mounjaro is a dual GIP and GLP-1 receptor agonist — it activates two hormone pathways. Wegovy is a GLP-1 agonist only. This dual mechanism in Mounjaro may help explain the slightly higher average weight loss seen in clinical trials, but both work by reducing appetite and increasing feelings of fullness.
Can I switch from Wegovy to Mounjaro or vice versa?
A prescriber can manage a switch between these medications if needed. There's no official conversion chart — switching must be done under medical supervision. Some approximate equivalence exists (Mounjaro 5 mg ≈ Wegovy 0.5 mg), but individual assessment is essential. Never switch without prescriber guidance.
How do I access Mounjaro or Wegovy on the NHS in the UK?
Ask your GP for a referral to your local tier 3 specialist weight management service. NHS availability varies significantly by region. Many areas have long waiting lists. Alternatively, you can access these weekly weight loss injections privately through a UK-licensed online prescriber following a clinical assessment, though this involves private costs.
Which weight loss injection should I choose?
Both Mounjaro and Wegovy are prescription-only medicines requiring a clinical assessment. Your prescriber will assess your medical history, health conditions, medications, and preferences to determine which is more suitable. Neither is universally "better" — suitability is individual. Use our free GLP-1 weight loss calculator above to explore potential outcomes with either medication.
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.