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 Max Dose vs Wegovy — What's the Difference?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight management injections available in the UK, but they work differently and reach different maximum doses. Mounjaro's maximum dose is 15 mg once weekly, whilst Wegovy's is 2.4 mg once weekly. This comparison guide explains how these medications differ, what the clinical evidence shows, and how your GP or prescriber will decide which might be suitable for you. Both require a clinical assessment before prescription, and results vary significantly between individuals.
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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.
Maximum Doses, Mechanisms, and Clinical Trial Results
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two separate hormone pathways to help regulate appetite and blood sugar. It reaches a maximum dose of 15 mg once weekly, administered via KwikPen. In the SURMOUNT-1 clinical trial, participants on the 15 mg dose lost an average of approximately 20.9% of their body weight over 72 weeks alongside a reduced-calorie diet and physical activity.
Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating a single hormone pathway. Its maximum dose is 2.4 mg once weekly in a pre-filled auto-injection pen. In the STEP-1 clinical trial, participants on 2.4 mg lost an average of approximately 14.9% of body weight over 68 weeks with the same lifestyle modifications.
Both medications start at lower doses and escalate gradually—Mounjaro begins at 2.5 mg, whilst Wegovy starts at 0.25 mg. Each dose is typically maintained for a minimum of 4 weeks before increasing, allowing your body to adjust and your prescriber to monitor tolerance.
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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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Eligibility and How Your Prescriber Decides
Eligibility for both medications is similar: UK adults with a BMI of 30 or above, or 27 or above with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. You can use our free BMI calculator to check your starting point instantly.
The choice between Mounjaro and Wegovy depends on individual factors including your medical history, any other medications you take, previous responses to GLP-1 medications, and prescriber preference. Neither medication is "better"—clinical trial results differ partly because they were conducted separately and measured slightly different populations. Your GP or licensed prescriber will assess which is more appropriate after a clinical consultation. Both are available through NHS specialist weight management services or private online prescribing with a clinical assessment.
- 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 key difference between Mounjaro and Wegovy?
Mounjaro is a dual GIP and GLP-1 agonist (activates two hormone pathways), whilst Wegovy is a GLP-1 agonist only (activates one pathway). Mounjaro reaches a higher maximum dose (15 mg vs 2.4 mg). Both are once-weekly injections and evidence suggests both can support weight loss when used alongside lifestyle changes.
Which medication causes more weight loss?
Clinical trials showed Mounjaro 15 mg resulted in approximately 20.9% average weight loss, whilst Wegovy 2.4 mg resulted in approximately 14.9% average weight loss. However, individual results vary significantly, and these trials were conducted separately. Your personal outcome depends on genetics, adherence, diet, and activity level.
How long does it take to reach the maximum dose?
Both medications escalate gradually. Mounjaro takes approximately 20 weeks to reach 15 mg (starting at 2.5 mg, increasing every 4 weeks). Wegovy takes approximately 16 weeks to reach 2.4 mg (starting at 0.25 mg). Your prescriber may adjust timelines based on how you tolerate each dose.
Are Mounjaro and Wegovy available on the NHS?
Both are approved for NHS prescription through specialist tier 3 weight management services. Access varies significantly by region and availability. Waiting lists can be lengthy. Both are also available privately through GPhC-registered pharmacies following an online clinical assessment and prescription.
Can you switch from one medication to the other?
Switching between Mounjaro and Wegovy is possible but must be managed by your prescriber. There is no official established conversion chart—your prescriber will assess the appropriate starting dose for the new medication based on your previous dose and tolerance. Never self-switch medications.
Ready to take control of your weight loss journey?
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