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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Does Wegovy Work The Same As Mounjaro?
Wegovy and Mounjaro are both prescription-only weight loss injections available in the UK, but they work in different ways. Wegovy (semaglutide) is a single GLP-1 receptor agonist, while Mounjaro (tirzepatide) activates two hormone pathways: GLP-1 and GIP. This means they have different mechanisms, dosing schedules, and average weight loss outcomes. Both require clinical assessment before prescription. Understanding the differences helps you and your GP decide which might be more suitable for your individual circumstances.
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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 The Two Medications Work Differently
Wegovy (semaglutide) is a GLP-1 receptor agonist — it activates a single natural hormone pathway in your body. This helps reduce appetite, increase feelings of fullness, slow stomach emptying, and improve blood sugar control. Wegovy is injected once weekly.
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two hormone pathways at once. The additional GIP mechanism may provide enhanced appetite suppression and better fat utilisation compared to single-pathway agents. Mounjaro is also injected once weekly.
Clinical trials show Mounjaro produces slightly higher average weight loss than Wegovy. In the SURMOUNT-1 trial, Mounjaro 15 mg achieved approximately 20.9% average body weight loss, whilst Wegovy's STEP-1 trial showed approximately 14.9% at the maximum dose. However, individual results vary significantly, and both medications work best alongside reduced-calorie diet 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.
Free Weight Loss Tools & Guides
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Dosing, Side Effects, And UK Access
Dosing differences: Wegovy starts at 0.25 mg and escalates to a maximum of 2.4 mg over 16 weeks. Mounjaro starts at 2.5 mg and escalates to a maximum of 15 mg over 20 weeks. Both use once-weekly KwikPen injections.
Both medications share similar common side effects — nausea, diarrhoea, vomiting, constipation, and stomach pain, particularly during dose escalation. In the UK, both require a prescription from a licensed prescriber following clinical assessment of eligibility (typically BMI ≥30, or BMI 27–29.9 with weight-related health conditions). Access is available through NHS specialist weight management services or private online prescribing. Your GP or prescriber can advise which option may be more suitable for your individual health profile and circumstances.
- 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 produces slightly higher average weight loss (approximately 21% vs 15% body weight), but individual results vary considerably. Effectiveness depends on your body, adherence, diet, and activity level. Your prescriber can discuss which might suit you best based on your medical history and goals.
Can you switch from Wegovy to Mounjaro or vice versa?
Yes, switching is possible and managed by your prescriber. There is no official conversion chart, but approximate equivalences exist (e.g., Wegovy 2.4 mg ≈ Mounjaro 10–15 mg). Any switch requires medical oversight to ensure safe transition and proper dose adjustment.
Are Wegovy and Mounjaro available on the NHS in the UK?
Both are licensed in the UK and NICE has approved tirzepatide for NHS use. However, NHS access is through specialist tier 3/4 weight management services, not standard GP prescription. Availability varies significantly by region. Waiting lists can be lengthy. Private access is available through online prescribing services.
What is the difference between Wegovy and Ozempic?
Both contain semaglutide, but Ozempic is licensed for type 2 diabetes (up to 2 mg dose) and is not licensed for weight loss in the UK. Wegovy is the licensed weight management version with a higher maximum dose (2.4 mg). Using Ozempic for weight loss is off-label and not recommended without specialist guidance.
How long do you need to take Wegovy or Mounjaro?
Both are intended as ongoing treatments. Weight typically returns if you stop the medication, so long-term use is expected. Your prescriber will monitor your progress and discuss how long treatment should continue based on your weight loss, side effects, and health outcomes. Use our free GLP-1 weight loss calculator to estimate potential results with these medications.
Ready to take control of your weight loss journey?
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