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 — Dose and Results Comparison
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight management injections available in the UK, but they work differently and have different dose ranges. Mounjaro is a dual GIP and GLP-1 receptor agonist that escalates to a maximum of 15 mg per week, while Wegovy is a GLP-1 agonist only, reaching a maximum of 2.4 mg per week. Understanding how these medications differ in mechanism, dosing, and clinical trial results can help you discuss options with your GP or prescriber. Both require a clinical assessment before prescription, and individual results vary significantly.
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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 Differ in Mechanism and Dosing
Mounjaro (tirzepatide) works as a dual GIP and GLP-1 receptor agonist, activating two natural hormone pathways simultaneously. This dual mechanism may explain why clinical trials showed slightly higher average weight loss compared to single-mechanism medications. Mounjaro escalates over approximately 20 weeks from a starting dose of 2.5 mg, titrating up by 2.5 mg increments every four weeks until reaching the maximum of 15 mg per week.
Wegovy (semaglutide) is a GLP-1 agonist only, activating a single hormone pathway. It escalates more gradually, starting at 0.25 mg and reaching its maximum of 2.4 mg over approximately 16 weeks. The STEP-1 clinical trial showed Wegovy helped participants lose an average of approximately 14.9% of body weight on the 2.4 mg dose alongside dietary and lifestyle changes.
In the SURMOUNT-1 trial, Mounjaro at 15 mg achieved average weight loss of approximately 20.9% body weight. Both medications require ongoing lifestyle changes and a reduced-calorie diet for optimal results.
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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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Which Medication Might Be Right for You — Individual Factors
Choosing between Mounjaro and Wegovy depends on individual health factors, not on one being universally "better." Your GP or prescriber will consider your medical history, current medications, any previous responses to GLP-1 therapy, and whether you have type 2 diabetes or prediabetes. Some people respond better to dual-mechanism medications like Mounjaro, whilst others achieve excellent results with single-mechanism Wegovy. Both are prescription-only and require a clinical assessment to determine eligibility and suitability.
Try our GLP-1 weight loss calculator to understand potential outcomes at different doses, and use our BMI calculator to establish your current health baseline. Your prescriber will personalise your treatment plan based on your individual needs, not on theoretical maximum results.
- 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 Mounjaro and Wegovy?
Mounjaro is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways. Wegovy is a GLP-1 agonist only. The dual mechanism in Mounjaro may produce slightly higher average weight loss in clinical trials, but individual results vary significantly and depend on many factors including adherence and lifestyle changes.
What are the maximum doses of each medication?
Mounjaro reaches a maximum of 15 mg per week, whilst Wegovy reaches a maximum of 2.4 mg per week. These cannot be directly compared as dosages because the medications work differently. Your prescriber will titrate you to the appropriate dose based on your response and tolerability.
Which medication caused more weight loss in clinical trials?
In SURMOUNT-1, Mounjaro at 15 mg showed average weight loss of approximately 20.9% body weight. In STEP-1, Wegovy at 2.4 mg showed average weight loss of approximately 14.9% body weight. However, these are average results from different trials — individual outcomes vary and depend on diet, exercise, genetics, and other factors.
Are both medications available on the NHS in the UK?
Both Mounjaro and Wegovy are licensed in the UK and available through NHS specialist tier 3 weight management services. However, NHS availability varies significantly by region, and waiting lists can be lengthy. Both are also available privately through GPhC-registered online pharmacies following a clinical assessment.
How long does it take to reach maximum dose?
Mounjaro takes approximately 20 weeks to titrate from 2.5 mg to 15 mg, escalating every four weeks. Wegovy takes approximately 16 weeks to reach 2.4 mg from 0.25 mg. Both require clinical assessment at each stage, and not all patients require or tolerate maximum doses.
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.