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 or Ozempic for Weight Loss — What's the Difference?
Both Mounjaro (tirzepatide) and Ozempic (semaglutide) are injectable medications used in weight management, but they work differently and have different uses in the UK. Ozempic is licensed for type 2 diabetes at doses up to 2 mg, while Mounjaro is specifically approved for weight loss. If you're considering a weekly weight loss injection, understanding how these medications differ is essential. Your GP or prescriber will assess which option, if any, is suitable for you based on your individual health profile and clinical needs.
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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 Ozempic Work Differently
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways simultaneously. This dual mechanism may help regulate appetite more effectively by working on two separate signals in your body.
Ozempic (semaglutide) is a GLP-1 receptor agonist only, activating a single hormone pathway. Wegovy also contains semaglutide but is specifically licensed for weight management in the UK, whereas Ozempic is licensed for type 2 diabetes.
Clinical trial data (SURMOUNT for Mounjaro, STEP for Wegovy) showed average weight loss of approximately 20.9% and 14.9% of body weight respectively, though individual results vary significantly. Both medications work alongside a reduced-calorie diet and increased physical activity. The choice between them depends on your health profile, not on one being universally "better" — your prescriber will assess which is appropriate for you.
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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.
UK Prescription and Access — What You Need to Know
In the UK, Ozempic is not licensed for weight loss — it's approved only for type 2 diabetes management. Using it for weight loss would be off-label and not recommended as a first-line weight loss treatment.
Mounjaro, as a weekly weight loss injection, is the appropriate option if you're considering tirzepatide for weight management. Wegovy (also semaglutide) is the licensed weight loss version of the GLP-1 medication.
Both Mounjaro and Wegovy require a UK prescription and clinical assessment. Access is available through NHS specialist tier 3 weight management services or private online prescribing following an assessment. Your GP or a licensed prescriber will evaluate your BMI, health conditions, and medical history to determine eligibility and suitability. Try our free GLP-1 weight loss calculator to estimate potential outcomes at different doses.
- 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 Ozempic used for weight loss in the UK?
No. Ozempic is licensed only for type 2 diabetes management in the UK and is not recommended as a weight loss treatment. Mounjaro and Wegovy are the prescription weight loss injections available. Using Ozempic off-label for weight loss is not standard practice or recommended.
What's the main difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) uses dual GIP and GLP-1 mechanisms, while Wegovy (semaglutide) uses GLP-1 only. Clinical trials showed Mounjaro may support slightly higher average weight loss, but individual results vary. Your prescriber will determine which suits your health profile.
How do I get Mounjaro or Wegovy on the NHS?
You'll need referral to a specialist tier 3 weight management service via your GP. Access varies by region and waiting lists can be lengthy. Private access is available through registered online prescribing services following a clinical assessment.
Can I switch from Ozempic to Mounjaro for weight loss?
If you're taking Ozempic for diabetes, any medication switch must be managed by your prescriber. Mounjaro is specifically designed for weight management and would require a new clinical assessment and prescription for weight loss purposes.
Which weight loss injection is better, Mounjaro or Wegovy?
Both are effective prescription medications with clinical trial support. "Better" depends on your individual health, medical history, and how your body responds. Your GP or prescriber will assess which is more appropriate for you during a clinical consultation.
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.