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 — Which is Right for You?
If you're researching weight loss injections in the UK, you've likely encountered both Mounjaro and Wegovy. Both are prescription-only GLP-1 receptor agonist medications approved for weight management in UK adults, yet they work differently and deliver different results. This guide explains the key differences, clinical trial data, and how to access both, so you can understand what your prescriber might recommend based on your individual circumstances.
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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.
Clinical Evidence and Mechanism: SURMOUNT vs STEP Trials
Mounjaro (tirzepatide) uses a dual GIP and GLP-1 receptor agonist mechanism — it activates two separate hormone pathways in the body. The SURMOUNT-1 clinical trial showed participants on the maximum 15mg dose lost an average of 20.9% of body weight over 72 weeks alongside diet and exercise.
Wegovy (semaglutide) is a GLP-1 receptor agonist only — activating a single hormone pathway. The STEP-1 clinical trial showed participants on the maximum 2.4mg dose lost approximately 14.9% of body weight over 68 weeks with the same lifestyle support.
- Mounjaro's dual mechanism may offer a stronger appetite-suppressing effect for some people
- Wegovy has longer real-world use data — semaglutide has been available longer than tirzepatide
- Both require a reduced-calorie diet and increased physical activity to be effective
- Individual results vary significantly — weight loss is not assured
Try our GLP-1 weight loss calculator above to estimate potential weight loss at different doses based on these trial averages.
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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.
Dosing, Administration, and Accessing Both in the UK
Mounjaro starts at 2.5mg weekly and escalates every 4 weeks up to a maximum of 15mg, delivered via a pre-filled KwikPen device. Wegovy starts at 0.25mg weekly and escalates more gradually to a maximum of 2.4mg, also once-weekly. Both are prescription-only medicines requiring a clinical assessment confirming your BMI and health circumstances.
In the UK, both can be accessed through NHS specialist tier 3 weight management services (typically with significant waiting lists) or through private online consultations with a UK-licensed prescriber. Your GP or prescriber will assess which medication — if either — suits your individual health profile, preferences, and any existing medical conditions. Neither medication is suitable during pregnancy or breastfeeding, and both may interact with certain medications, particularly oral contraceptives and diabetes treatments.
- 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 stronger than Wegovy?
Clinical trials show Mounjaro produced greater average weight loss (20.9% vs 14.9%), but this doesn't mean it's "stronger" for everyone. Individual response varies. The dual mechanism may suit some people better than others. Your prescriber will recommend based on your health profile, not trial averages alone.
Can I switch from Wegovy to Mounjaro?
Yes, some people do switch. There's no official conversion chart, but approximate equivalence exists (e.g., Wegovy 2.4mg ≈ Mounjaro 10–15mg). Any switch must be managed by your prescriber and is not a simple substitution — it requires reassessment and potentially a restart of the dose escalation schedule.
Which is easier to get on the NHS?
Both face similar NHS access barriers — both require referral to specialist tier 3 weight management services. Regional availability and waiting times vary. Mounjaro is newer, so some areas may have protocols in place for Wegovy first. Ask your GP about your local service's current formulary preferences.
What if I have type 2 diabetes — does that change which I can take?
Both are licensed for weight management in adults with or without type 2 diabetes. However, if you're taking insulin or sulphonylurea medications, your prescriber will need to adjust doses to prevent low blood sugar. Always disclose all medications during your clinical assessment.
How long do I need to take Mounjaro or Wegovy?
Both are designed for long-term use. If you stop, weight typically returns. Many people continue indefinitely at a maintenance dose. Your prescriber will discuss the expected duration with you during your assessment — it's not a short-term course like antibiotics.
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.