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 Suits Your Diet Plan?
If you're comparing Mounjaro and Wegovy as part of your weight management plan, understanding how each medication works is essential. Both are prescription-only injections licensed in the UK for weight loss, but they have different mechanisms and trial outcomes. This guide compares both medications factually to help you understand what your GP or prescriber might recommend based on your individual health needs and clinical assessment.
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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.
Clinical Trial Data and Mechanism Differences
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — meaning it activates two natural hormone pathways simultaneously. In the SURMOUNT-1 clinical trial, participants lost an average of 15% body weight at 5mg, 19.5% at 10mg, and 20.9% at 15mg over 72 weeks, alongside reduced-calorie diet and increased physical activity. Wegovy (semaglutide) is a GLP-1-only agonist. The STEP-1 trial showed approximately 14.9% average body weight loss at the maximum 2.4mg dose over 68 weeks with the same lifestyle support.
The key difference: Mounjaro's dual mechanism may contribute to slightly higher average weight loss in trials, though individual results vary significantly. Both slow gastric emptying and reduce appetite, supporting adherence to reduced-calorie diet plans. Neither is a substitute for dietary changes — both are used alongside a structured eating plan and increased physical activity.
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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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Suitability, Prescribing, and Your Diet Plan
Your prescriber will assess which medication suits you based on your medical history, BMI, and any weight-related health conditions. Use our free GLP-1 weight loss calculator above to estimate potential outcomes at different doses with either medication — this can help you understand projected results when discussing options with your GP or specialist.
Both Mounjaro (via its KwikPen device) and Wegovy require a prescription and clinical assessment. UK eligibility is the same: BMI 30 or above, or 27–29.9 with weight-related conditions like type 2 diabetes or high blood pressure. Prescribing in the NHS goes through specialist tier 3 services; private access is available through licensed UK prescribers. Your diet plan success depends more on consistent adherence than which medication you use.
- 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 more effective than Wegovy for weight loss?
Clinical trials show Mounjaro produced slightly higher average weight loss (up to 20.9%) compared to Wegovy (14.9%), but individual results vary significantly. Effectiveness depends on your adherence to diet and lifestyle changes, not the medication alone. Your prescriber will recommend based on your specific health profile, not trial averages.
Can I download a Mounjaro diet plan PDF from MyWeightCheck?
MyWeightCheck provides educational information, not personalised diet plans. Your GP or a registered dietitian should create a diet plan tailored to your needs if you're prescribed Mounjaro or Wegovy. The NHS and specialist weight management services often provide guidance on eating plans alongside these medications.
What's the difference between Mounjaro's GIP+GLP-1 mechanism and Wegovy's GLP-1 only?
Mounjaro activates two hormone pathways (GIP and GLP-1), while Wegovy activates GLP-1 only. This dual action may explain Mounjaro's slightly higher trial weight loss, but both medications work by reducing appetite and supporting feeling fuller after smaller meals alongside a reduced-calorie diet.
Do I need a prescription for both Mounjaro and Wegovy in the UK?
Yes, both are prescription-only medicines requiring a clinical assessment. Mounjaro uses a KwikPen device injected once weekly, as does Wegovy. Access is through NHS specialist services or private prescribing via a UK-licensed prescriber. Your GP cannot prescribe these directly — referral to tier 3 weight management services is typically required on the NHS.
How do diet plans work alongside Mounjaro or Wegovy?
Neither medication works without dietary changes. Both are prescribed alongside a reduced-calorie diet (typically 500–750 kcal deficit daily) and increased physical activity. Use our BMI calculator and progress tracker above to monitor your weight alongside your eating plan. Results depend on consistent lifestyle changes, not medication alone.
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.