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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Is Mounjaro Semaglutide? Understanding the Difference
No, Mounjaro is not semaglutide — they are two distinct prescription-only weight loss medications licensed in the UK. Both are GLP-1-based injectables, but Mounjaro (tirzepatide) works differently from Wegovy (semaglutide) because it activates two hormone pathways instead of one. This guide explains the key differences, clinical trial outcomes, and how your GP or prescriber decides which might suit your health needs. Use our free BMI calculator above to check your starting point, then explore how these medications compare.
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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 Mounjaro and Semaglutide Differ: Mechanism and Trial Data
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two natural hormone pathways that regulate appetite and blood sugar. Wegovy (semaglutide) is a GLP-1-only receptor agonist — it activates one pathway. In the SURMOUNT-1 clinical trial, Mounjaro at the maximum 15 mg dose produced average weight loss of approximately 20.9% of body weight over 72 weeks. In the STEP-1 trial, semaglutide at 2.4 mg produced average weight loss of approximately 14.9% over 68 weeks. Both results were achieved alongside a reduced-calorie diet and increased physical activity — individual results vary significantly. The dual mechanism may explain Mounjaro's slightly higher average weight loss, though clinical effectiveness depends on individual response. A prescriber will assess which medication aligns with your specific health profile, considering factors like existing conditions, other medications, and your weight loss goals.
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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 Medication Is Right for You? Prescriber Assessment
Choosing between Mounjaro and semaglutide is a clinical decision made by your GP or licensed prescriber based on your health history, BMI, and weight-related conditions. Both require a prescription and clinical assessment in the UK. Eligibility typically includes a BMI of 30 kg/m² or above, or BMI 27–29.9 with weight-related health conditions (lower thresholds apply for South Asian, Chinese, Black African, or Black Caribbean adults). Access through NHS specialist tier 3 services varies by region; private prescription is available through accredited online services. Your prescriber will consider your medical history, current medications, any contraindications, and personal preference. Try our free GLP-1 weight loss calculator to estimate potential outcomes at different doses of either medication, then discuss findings with your healthcare provider.
- 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 the same as semaglutide?
No. Mounjaro (tirzepatide) and Wegovy (semaglutide) are different medications with different mechanisms. Mounjaro is a dual GIP+GLP-1 agonist; semaglutide is a GLP-1-only agonist. Both are licensed for weight loss in the UK, but they work differently and have different dose ranges and trial outcomes.
Which produces more weight loss — Mounjaro or semaglutide?
Clinical trials suggest Mounjaro may produce slightly higher average weight loss (approximately 15–21% body weight) compared to semaglutide (approximately 14.9% body weight). However, individual results vary significantly, and real-world effectiveness depends on adherence, lifestyle changes, and personal response. Your prescriber will advise which is suitable for you.
What is the maximum dose of Mounjaro versus Wegovy?
Mounjaro (tirzepatide) has a maximum dose of 15 mg once weekly. Wegovy (semaglutide) has a maximum dose of 2.4 mg once weekly. Both start at lower doses and are titrated upwards over weeks — the dose titration schedule differs between the two medications.
Can I switch from semaglutide to Mounjaro or vice versa?
Switching between medications is possible but must be managed by your prescriber. There is no official established conversion between doses. Any change requires a clinical reassessment and a new prescription. Do not switch without speaking to your GP or prescriber first.
How do I access Mounjaro or semaglutide in the UK?
Through NHS tier 3 specialist weight management services (requires GP referral; availability varies by region) or privately through a UK-licensed prescriber following an online clinical assessment. Both routes require a prescription. Use our free BMI calculator to check your eligibility starting point, then contact your GP or explore private options.
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.