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 Weight Loss Injection?
If you're considering prescription weight loss treatment in the UK, you'll likely encounter both Mounjaro (tirzepatide) and Wegovy (semaglutide). Both are licensed for weight management in UK adults, but they work slightly differently and have different dosing schedules. Understanding the key differences helps you have an informed conversation with your GP or prescriber. This guide compares both medications factually — which one is suitable depends on your individual health profile 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.
How Mounjaro and Wegovy Work — Key Differences
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two different hormone pathways in the body. This combination may help regulate appetite more intensely than a single pathway.
Wegovy (semaglutide) is a GLP-1 receptor agonist only — it targets the GLP-1 hormone pathway that signals fullness to the brain and slows gastric emptying.
Clinical trial data shows both support weight loss alongside reduced-calorie diet and increased physical activity. In the SURMOUNT trial, Mounjaro at the maximum 15mg dose helped participants lose an average of approximately 20.9% of body weight over 72 weeks. The STEP-1 trial showed Wegovy at 2.4mg resulted in approximately 14.9% average weight loss over 68 weeks. Individual results vary significantly — these are trial averages, not assures.
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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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Dosing, Access, and Suitability — What Your Prescriber Considers
Mounjaro is dosed from 2.5mg to a maximum of 15mg weekly, with dose increases every 4 weeks. Wegovy is dosed from 0.25mg to a maximum of 2.4mg weekly, with slower dose escalation. Both are once-weekly injections available via NHS specialist services or private prescribing following clinical assessment.
Your prescriber will choose based on your medical history, current medications, and individual health needs — neither is objectively "better". Both require a UK-licensed prescription. Try our free GLP-1 weight loss calculator to explore potential weight loss projections at different doses. Your GP or prescriber can discuss which mechanism and dosing schedule suits you best.
- 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?
Clinical trials show both support weight loss. Mounjaro's dual mechanism may produce slightly higher average weight loss in trials, but individual results vary considerably. Effectiveness depends on your personal response, adherence, and lifestyle changes alongside medication. Your prescriber will assess which is more suitable for your health profile.
What's the main difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) activates two hormone pathways — GIP and GLP-1. Wegovy (semaglutide) activates GLP-1 only. Both reduce appetite and support feeling fuller. Mounjaro has higher maximum doses and may achieve more weight loss on average, but both require prescription and clinical assessment.
Can I switch from Wegovy to Mounjaro or vice versa?
Switching between GLP-1 medications must be managed by your prescriber. There's no official established conversion chart — approximate equivalences exist but any switch requires clinical guidance. Your GP or prescriber will assess whether a change is appropriate based on your response and side effects.
How do I access Mounjaro or Wegovy on the NHS in the UK?
Both are available through NHS specialist tier 3 weight management services — you'll typically need a GP referral. Waiting lists and availability vary significantly by region. Both are also available privately through UK-licensed prescribers following an online clinical assessment.
Which injection has fewer side effects — Mounjaro or Wegovy?
Both commonly cause nausea, diarrhoea, constipation, and stomach discomfort, especially at the start. Individual tolerance varies — some people manage side effects better with one medication than the other. This is another factor your prescriber considers. Side effect profiles are similar, so choice often depends on other clinical factors.
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.