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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Should I Use Mounjaro or Wegovy?
Deciding whether to use Mounjaro (tirzepatide) or Wegovy (semaglutide) depends on your individual health profile, eligibility, and what your prescriber recommends following a clinical assessment. Both are prescription-only weight management injections licensed in the UK, but they work differently and have different dose ranges. This guide explains the key differences so you can understand what your GP or prescriber might discuss with you — and why one may be more suitable than the other for your specific situation.
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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 Differently
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two separate hormone pathways in your body. This dual mechanism may contribute to slightly stronger appetite suppression and weight loss in clinical trials. Wegovy (semaglutide) is a GLP-1 receptor agonist only — it activates a single hormone pathway. Both slow gastric emptying and support feeling fuller after meals, but the addition of GIP activation in Mounjaro is its key distinction.
Clinical trial data shows these differences in outcomes: in the SURMOUNT-1 trial, participants on 15mg Mounjaro lost an average of approximately 20.9% of their body weight over 72 weeks. In the STEP-1 trial, participants on 2.4mg Wegovy lost approximately 14.9% of body weight over 68 weeks. However, individual results vary significantly — these are averages, not assures.
Both medications are given as once-weekly injections. Mounjaro has a wider dose range (2.5mg to 15mg) compared to Wegovy (0.25mg to 2.4mg), which means more flexibility in titration for Mounjaro.
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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.
Which One Might Be Right for You?
Your prescriber will assess your medical history, current medications, BMI, weight-related health conditions, and contraindications to decide which medication is appropriate. Both are suitable for adults with a BMI of 30 or above, or 27–29.9 with weight-related conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. If you have a history of certain gastrointestinal conditions, pancreatitis, or thyroid concerns, your prescriber may recommend one over the other. Use our free GLP-1 weight loss calculator above to explore projected outcomes with either medication, and our BMI calculator to confirm your current BMI category. Ultimately, the choice is made collaboratively between you and your prescriber based on clinical suitability, not personal preference alone.
- 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 suggest Mounjaro may result in slightly greater average weight loss (approximately 20.9% vs 14.9%), but individual results vary considerably. "More effective" is not accurate — both are effective for some people and less so for others. Your prescriber will choose based on what's clinically suitable for you, not just efficacy data.
Can I switch from Wegovy to Mounjaro or vice versa?
Switching between medications must always be managed by your prescriber. There is no official established conversion chart — approximate equivalences exist (5mg Mounjaro ≈ 0.5mg Wegovy), but any switch requires medical supervision, a washout period may be needed, and you would typically restart titration.
What are the main side effects of each?
Both share common side effects: nausea, diarrhoea, vomiting, constipation, and stomach pain — most common in early weeks. Side effect profiles are very similar; individual tolerance varies. Your prescriber will discuss this during your assessment.
How do I know my eligibility for either medication?
UK adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions (type 2 diabetes, high blood pressure, cardiovascular disease, sleep apnoea), may be eligible. South Asian, Chinese, Black African, and Black Caribbean adults may have lower BMI thresholds. Only a prescriber can confirm your eligibility following assessment.
Are both available on the NHS?
Both Mounjaro and Wegovy are available through NHS specialist tier 3 weight management services, but availability and waiting times vary significantly by region. Private access is available through UK-licensed online prescribers without NHS referral. Ask your GP about local NHS options or explore private pathways if waiting times are long in your area.
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.