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
Free tracker included with every download this week
Mounjaro Pen Extra Dose vs Wegovy — What's the Difference?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight loss injections available in the UK, but they work differently and have different maximum doses. Mounjaro reaches 15 mg per week, whilst Wegovy's highest dose is 2.4 mg per week. This guide compares the two medications side-by-side, explains their different mechanisms, and helps you understand how your GP or prescriber will assess which is suitable for you. Both require clinical assessment and are used alongside lifestyle changes.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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 Wegovy Differ — Clinical Trial Evidence
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways to regulate appetite and support fullness. In the SURMOUNT-1 clinical trial, participants on the maximum 15 mg dose lost an average of 20.9% of their body weight over 72 weeks, whilst those on 10 mg lost approximately 19.5%.
Wegovy (semaglutide) is a single GLP-1 receptor agonist — it activates only the GLP-1 pathway. In the STEP-1 clinical trial, the maximum 2.4 mg dose resulted in an average weight loss of approximately 14.9% over 68 weeks. Both medications are prescribed using a titration schedule, starting at low doses and increasing gradually every 4 weeks (for Mounjaro) or every 4 weeks initially (for Wegovy), allowing your body to adjust.
Important context: these are clinical trial averages alongside reduced-calorie diet and increased physical activity. Individual results vary significantly, and weight loss is not assured.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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
Your prescriber — whether on the NHS through a specialist weight management service or via a private online consultation — will assess which medication suits your individual health profile. Both are eligible for adults with a BMI of 30 or above, or 27–29.9 with weight-related conditions like type 2 diabetes, hypertension, or cardiovascular disease. Your prescriber will consider your medical history, other medications, and personal preferences.
Neither medication is superior universally — some individuals respond better to Mounjaro's dual mechanism, whilst others find Wegovy equally effective. Lower starting doses mean gradual tolerance-building with both. Use our free GLP-1 weight loss calculator to explore potential outcomes at different doses, and our BMI calculator to check where you stand against UK health thresholds.
- 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+GLP-1 agonist (activates two hormone pathways), whilst Wegovy is a GLP-1-only agonist. Mounjaro reaches a higher maximum dose (15 mg vs 2.4 mg) and showed slightly higher average weight loss in clinical trials — approximately 20.9% vs 14.9% — but individual results vary.
Can I switch from Wegovy to Mounjaro?
Yes, switching is possible and should be managed by your prescriber. Approximate dose equivalences exist (e.g., Wegovy 2.4 mg is roughly comparable to Mounjaro 10 mg), but any switch requires clinical guidance to ensure safe transition and appropriate re-titration.
Does the NHS prescribe both Mounjaro and Wegovy?
Both are approved by NICE for NHS use within specialist tier 3 weight management services. However, NHS availability varies significantly by region and ICB funding. Many areas have long waiting lists. Private online prescribing offers faster access through GPhC-registered pharmacies.
Which injection causes fewer side effects, Mounjaro or Wegovy?
Both medications commonly cause nausea, diarrhoea, and constipation, especially at higher doses. Side effect profiles are similar. Individual tolerance varies — some people tolerate one better than the other. Your prescriber can discuss this during assessment.
How long does a Mounjaro pen last compared to Wegovy?
Each Mounjaro KwikPen contains 4 weekly doses (approximately 4 weeks supply). Wegovy pens also contain 4 weekly doses. Both are used once weekly. Repeat prescriptions are needed monthly to maintain continuous treatment.
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.