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 Does Monjaro Do — How It Compares to Wegovy
Monjaro (tirzepatide) is a prescription-only weight loss injection that works differently from other GLP-1 medications. Unlike Wegovy, which uses a single GLP-1 receptor agonist mechanism, Monjaro is a dual GIP and GLP-1 receptor agonist, meaning it activates two separate hormone pathways in your body. This dual action may help regulate appetite, reduce cravings, and support feeling fuller after meals. Both are once-weekly injections licensed in the UK for weight management in adults, but they work through different mechanisms. Understanding how Monjaro works and how it compares to alternatives like Wegovy can help you and your prescriber decide which option might be most suitable for your individual needs.
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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 Monjaro Works vs Wegovy — Clinical Trial Evidence
Monjaro's dual mechanism: Monjaro activates both GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 receptors. GIP helps regulate fat storage and utilisation, while GLP-1 signals to the brain that you're full and slows gastric emptying. This dual action may offer additional benefits compared to single-mechanism medications.
Wegovy's single mechanism: Wegovy (semaglutide) activates only the GLP-1 receptor, which reduces appetite and supports feeling fuller faster.
Clinical trial results: In the SURMOUNT-1 trial, participants on 15mg Monjaro achieved an average weight loss of approximately 20.9% of body weight over 72 weeks. In the STEP-1 trial, Wegovy (2.4mg) showed average weight loss of around 14.9% over 68 weeks. Both trials included reduced-calorie diet and increased physical activity. Individual results vary significantly — these are averages, not assured outcomes.
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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.
Which Might Suit You — A Prescriber Decision
Both Monjaro and Wegovy are prescription-only medicines that require a clinical assessment before dispensing. Your prescriber will evaluate your medical history, current health conditions, medications, and personal preferences to recommend the most suitable option for you. Neither medication is "better" — suitability depends on your individual circumstances. Some people respond better to dual-mechanism treatment, while others achieve excellent results with single-mechanism GLP-1 therapy. You can use our free GLP-1 weight loss calculator to estimate potential weight loss at different doses, and our BMI calculator to check your starting point. Whichever you're prescribed, success depends on combining medication with sustained dietary changes and increased physical activity.
- 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's the main difference between Monjaro and Wegovy?
Monjaro is a dual GIP+GLP-1 receptor agonist, activating two hormone pathways. Wegovy is a GLP-1-only receptor agonist, activating one pathway. This dual mechanism in Monjaro may offer different effects, but both can support weight loss when combined with lifestyle changes.
Which showed better weight loss in clinical trials?
Monjaro (15mg) showed average weight loss of 20.9% in SURMOUNT-1, and Wegovy (2.4mg) showed 14.9% in STEP-1. However, clinical trial averages don't predict individual outcomes. Results vary significantly between people, and both medications can be effective.
Can I switch from one to the other?
Switching between Monjaro and Wegovy requires prescriber guidance. There's no official conversion chart — your prescriber will assess your response and adjust dosing accordingly. Never switch medications without medical supervision.
How often do I inject Monjaro vs Wegovy?
Both are once-weekly injections. Monjaro is available as the KwikPen device with doses ranging from 2.5mg to 15mg. Wegovy doses range from 0.25mg to 2.4mg. Both require a minimum 4 weeks at each dose before increasing.
Do I need NHS referral to access either medication?
NHS access requires referral to a specialist tier 3 weight management service — availability varies by region and waiting times can be long. Private access is available through a UK-licensed prescriber following an online assessment with a GPhC-registered pharmacy.
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.