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 Ozempic for Weight Loss in the UK
Both Mounjaro and Ozempic contain similar active ingredients but are licensed for different purposes in the UK. Mounjaro (tirzepatide) is specifically approved for weight management, while Ozempic (semaglutide) is licensed for type 2 diabetes — not weight loss. This guide explains the key differences, how each works, and what NHS and private options are available to you. Understanding which medication is appropriate requires a clinical assessment from a qualified prescriber.
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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.
Key Differences Between Mounjaro and Ozempic
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two natural hormone pathways to help regulate appetite and support feeling fuller after meals. It's approved in the UK specifically for weight management in adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions. The starting dose is 2.5 mg once weekly, escalating to a maximum of 15 mg weekly.
Ozempic (semaglutide) is a GLP-1 receptor agonist licensed in the UK for type 2 diabetes management at doses up to 2 mg. It is not licensed for weight loss in the UK, though it may be used off-label in specialist settings. Using Ozempic for weight loss outside of approved diabetes treatment is off-label prescribing.
- Mounjaro: dual mechanism, higher maximum dose (15 mg), weight-specific approval
- Ozempic: single GLP-1 mechanism, lower maximum dose (2 mg), diabetes-specific approval
- Clinical trials showed Mounjaro may produce greater average weight loss than single GLP-1 medications
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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.
NHS Access and UK Prescribing Context
On the NHS, access to weight management medications is through tier 3 specialist weight management services, typically following referral from your GP. NICE has approved tirzepatide (Mounjaro) for use within these services for eligible adults. However, NHS availability varies significantly by region, and waiting lists can be substantial.
Ozempic prescribed for weight loss would be off-label and is not part of standard NHS weight management pathways. If you have type 2 diabetes and are prescribed Ozempic, your GP can advise whether it's appropriate for your condition. For weight loss specifically, you can discuss Mounjaro eligibility with your GP or access it through private prescribing following a clinical assessment by a UK-licensed prescriber.
- NHS route: referral to tier 3 services, eligibility assessed by specialists
- Private route: online consultation with UK prescriber, available without NHS referral
- Individual results vary; both require lifestyle changes alongside medication
- 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 licensed for weight loss in the UK?
No. Ozempic is licensed in the UK for type 2 diabetes management only, at doses up to 2 mg weekly. It is not an approved weight loss medication in the UK. Using it for weight loss is off-label prescribing and is not part of standard NHS weight management guidelines.
Why is Mounjaro more effective for weight loss than Ozempic?
Mounjaro uses a dual GIP and GLP-1 mechanism, while Ozempic uses GLP-1 only. Clinical trials showed Mounjaro produced an average weight loss of 15–21% of body weight, compared to approximately 15% for GLP-1-only medications. However, individual results vary significantly and depend on diet, activity, and personal factors.
Can I get Mounjaro on the NHS for weight loss?
Mounjaro is available on the NHS through tier 3 specialist weight management services. You'll need a referral from your GP and assessment by specialists. Eligibility requires a BMI of 30 or above, or 27–29.9 with weight-related health conditions. Availability and waiting times vary by region.
What's the difference between Mounjaro and Wegovy?
Both are approved for weight loss in the UK. Wegovy (semaglutide) is a GLP-1 agonist with a maximum dose of 2.4 mg weekly. Mounjaro is a dual GIP/GLP-1 agonist with a maximum dose of 15 mg weekly. Clinical trials suggest Mounjaro may produce slightly greater average weight loss, though results vary between individuals.
How do I check if I'm eligible for weight loss medication?
Use our free BMI calculator above to check your BMI, then discuss eligibility with your GP. You may qualify if your BMI is 30 or above, or 27–29.9 with conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. Your prescriber will assess your full health history before recommending treatment.
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.