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 5th Dose vs Wegovy — How They Compare
When you reach the 5th dose of Mounjaro (15 mg once weekly), you've reached the maximum strength of tirzepatide. Many people wonder how this compares to Wegovy, which uses a different medication called semaglutide. Both are prescription-only weight management injections licensed in the UK, but they work via different mechanisms. Understanding the key differences can help you and your prescriber make an informed decision about which might be most suitable for your individual health 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.
Key Differences: Mechanism and Clinical Trial Data
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two natural hormone pathways, which is what sets it apart from other weight loss injections. At the maximum 15 mg dose, clinical trial data (SURMOUNT-1) showed an average weight loss of approximately 20.9% of body weight over 72 weeks, alongside a reduced-calorie diet and increased physical activity. Individual results vary significantly.
Wegovy (semaglutide) is a GLP-1 receptor agonist only — it works via a single hormone pathway. At the maximum 2.4 mg dose, the STEP-1 trial showed an average weight loss of approximately 14.9% of body weight over 68 weeks, under similar lifestyle conditions. Again, individual results differ widely.
- Mounjaro: dual mechanism (GIP + GLP-1)
- Wegovy: single mechanism (GLP-1 only)
- Both require prescription and clinical assessment
- Trial data shows different average outcomes, but personal response varies
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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 Is Right for You? — A Prescriber Decision
Both Mounjaro and Wegovy are licensed for UK adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. The choice between them isn't about one being universally "better" — it's about individual suitability. Your prescriber will assess your medical history, current medications, and health goals to recommend the most appropriate option.
Some people respond better to one mechanism than another, and tolerability varies individually. If you've tried one and want to explore the other, your GP or prescriber can help you switch safely. You can use our free GLP-1 weight loss calculator to estimate potential outcomes at different doses of either medication, though actual results depend on your body and lifestyle choices.
- 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 15 mg stronger than Wegovy 2.4 mg?
They use different mechanisms and doses aren't directly comparable. Trial data shows Mounjaro 15 mg achieved higher average weight loss (20.9%) than Wegovy 2.4 mg (14.9%), but individual results vary. Some people respond better to one than the other. Your prescriber assesses which suits you.
What's the difference between Mounjaro's dual mechanism and Wegovy's single mechanism?
Mounjaro activates both GIP and GLP-1 hormone pathways, while Wegovy activates GLP-1 only. The dual mechanism may explain Mounjaro's higher average trial outcomes, but both help reduce appetite and support weight loss. Individual response varies.
Can I switch from Mounjaro to Wegovy or vice versa?
Yes, you can switch between them, but this must be managed by your prescriber. There's no official conversion chart — your prescriber will assess the appropriate dose and timing for a safe switch based on your health and response.
How long does it take to reach Mounjaro's 5th dose?
Each dose increase requires at least 4 weeks. So reaching the 5th dose (15 mg) takes approximately 20 weeks — about 5 months — if you escalate every 4 weeks: 2.5 mg, 5 mg, 7.5 mg, 10 mg, then 15 mg.
Do Mounjaro and Wegovy have the same side effects?
Both commonly cause nausea, diarrhoea, constipation, and stomach pain — especially when starting or increasing doses. Serious side effects are rare but similar (pancreatitis, gallbladder issues). Individual tolerability varies. Always discuss side effects with your prescriber.
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.