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 Diet Plan vs Wegovy — What's the Difference?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight management injections used alongside diet and exercise in the UK. While they work similarly to reduce appetite and support weight loss, they use different mechanisms and show different results in clinical trials. Understanding how they compare can help you and your prescriber decide which might be right for you. Both require a clinical assessment before prescription, and individual results vary significantly. Try our free GLP-1 weight loss calculator to estimate potential outcomes with different medications.
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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 Wegovy Work — Mechanism and Trial Data
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two natural hormone pathways rather than one. In the SURMOUNT-1 clinical trial, participants receiving the maximum 15mg dose lost an average of 20.9% of their body weight over 72 weeks alongside reduced-calorie diet and physical activity.
Wegovy (semaglutide) is a single GLP-1 receptor agonist. In the STEP-1 clinical trial, the maximum 2.4mg dose resulted in approximately 14.9% average body weight loss over 68 weeks with the same lifestyle support.
The dual mechanism of Mounjaro may explain slightly higher average weight loss in trials, though both medications are effective. Important context: these are clinical trial averages, individual results vary, and neither assures specific outcomes. Both are prescription-only and require a clinical assessment to determine suitability. Use our free BMI calculator to check your current BMI category — this helps determine eligibility for either medication in the UK.
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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, Side Effects, and Suitability — Which Is Right for You?
Dosing schedules differ: Mounjaro doses range from 2.5mg to 15mg weekly, with minimum 4 weeks at each dose before escalating. Wegovy starts at 0.25mg and escalates to a maximum of 2.4mg weekly. Both are once-weekly injections.
Side effects are similar — nausea, diarrhoea, constipation, and stomach pain are most common with both medications. The choice between them is a clinical decision made with your prescriber based on your health history, preferences, and NHS or private access availability.
Both Mounjaro and Wegovy require a UK-licensed prescriber's assessment. NHS access is through specialist tier 3 weight management services; private access is through online prescribing services. Your prescriber will consider your BMI, health conditions, current medications, and any contraindications. Neither medication is assured to produce specific weight loss results — they're tools to support a reduced-calorie diet and increased physical activity. Track your progress with our free progress tracker.
- 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.
Which loses more weight — Mounjaro or Wegovy?
Clinical trials show Mounjaro resulted in slightly higher average weight loss (20.9% at maximum dose) compared to Wegovy (14.9%). However, these are trial averages. Individual results vary significantly based on diet, exercise, adherence, and personal metabolism. Your prescriber will discuss expected outcomes for your situation.
Can I switch from Wegovy to Mounjaro?
Yes, switching is possible and managed by your prescriber. There is no official established conversion chart between the medications — your prescriber will guide safe transition. Approximate rough equivalences exist but are not clinically standardised. Never attempt to switch doses without guidance.
How do I access Mounjaro or Wegovy on the NHS in the UK?
Both medications are available through NHS specialist tier 3 weight management services. You'll need a GP referral. Availability and waiting times vary significantly by region and NHS integrated care board. Private access is available through GPhC-registered pharmacies following an online prescriber consultation.
Which medication has fewer side effects?
Both have very similar side effect profiles — nausea, diarrhoea, and constipation are common with both. Side effect severity varies between individuals. Your prescriber will discuss potential side effects and management strategies. Starting at a low dose and gradually increasing reduces side effect intensity for most people.
Are Mounjaro and Wegovy suitable if I have type 2 diabetes?
Both can be prescribed to people with type 2 diabetes or prediabetes, and may help with blood sugar control. However, if you take insulin or certain diabetes medications, dose adjustments may be needed. Always inform your prescriber of all medications. Individual suitability requires a clinical assessment.
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.