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
Free tracker included with every download this week
What Is Mounjaro Used For?
Mounjaro (tirzepatide) is a prescription-only weight management injection licensed in the UK for adults with obesity or overweight with weight-related health conditions. It works by activating two natural hormone pathways — GIP and GLP-1 — to help reduce appetite and support feeling fuller after meals. Clinical trials showed that Mounjaro may help participants lose an average of 15–21% of their body weight, though individual results vary significantly. It's always used alongside a reduced-calorie diet and increased physical activity, not as a standalone treatment. Your GP or a licensed prescriber will assess whether Mounjaro is suitable for you based on your personal health profile.
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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 Works and Who Can Use It
Mounjaro contains tirzepatide, a dual GIP and GLP-1 receptor agonist. Unlike Wegovy (which activates GLP-1 only), Mounjaro's dual mechanism may offer additional benefits in appetite regulation and metabolic support. The medication is delivered via a once-weekly injection using a convenient KwikPen device.
In the UK, you may be eligible for Mounjaro if you have a BMI of 30 or above, or a BMI of 27–29.9 with weight-related health conditions such as type 2 diabetes, prediabetes, high blood pressure, abnormal blood fats, sleep apnoea, or cardiovascular disease. South Asian, Chinese, Black African, and Black Caribbean adults may have access at lower BMI thresholds (27.5+) due to higher health risks at lower weights.
Use our free BMI calculator above to check whether your BMI falls within typical eligibility ranges. Mounjaro requires a prescription and clinical assessment — you cannot obtain it without a prescriber's evaluation. Access is available through NHS specialist weight management services or private online prescribing following a consultation.
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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.
Mounjaro Doses, Side Effects, and Comparisons
Mounjaro comes in doses ranging from 2.5 mg (starting dose) to 15 mg (maximum maintenance dose), with dose increases every 4 weeks. Common side effects include nausea, diarrhoea, vomiting, and constipation — most improve over time as your body adjusts. Our GLP-1 weight loss calculator can help you estimate potential weight loss outcomes at different doses based on clinical trial data.
When comparing Mounjaro to Wegovy (semaglutide), both are once-weekly injections licensed for weight management in the UK. Mounjaro's dual mechanism may deliver slightly higher average weight loss (15–21% vs ~15% for Wegovy), but both require prescription and clinical assessment. The choice between them depends on your personal health profile and prescriber guidance — there is no "better" option universally.
- 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 the same as Ozempic?
Both contain semaglutide, but Mounjaro is not the same as Ozempic. Mounjaro contains tirzepatide, a different medication. Ozempic (semaglutide) is approved for type 2 diabetes, not weight loss. Wegovy is the licensed weight management version of semaglutide in the UK. Always check the brand name on your prescription.
How quickly will I lose weight on Mounjaro?
Weight loss timelines vary. Clinical trials showed average weight loss of 15–21% of body weight over approximately 72 weeks at maximum dose. Most weight loss occurs between weeks 8 and 32. Results depend on your starting weight, dose, diet adherence, and physical activity. Individual results vary significantly.
Can I get Mounjaro on the NHS in the UK?
Mounjaro is approved by NICE for NHS specialist weight management services, but access varies by region and availability. You typically need a GP referral to tier 3 or 4 specialist services. Waiting lists can be lengthy. Private prescribing through online consultations is also available without NHS referral.
What makes Mounjaro different from other weight loss injections?
Mounjaro is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways simultaneously. Wegovy (semaglutide) activates GLP-1 only. This dual mechanism in Mounjaro may contribute to its slightly higher average weight loss in clinical trials, though both are effective prescription treatments.
Is Mounjaro safe to use long-term?
Clinical data supports long-term use of Mounjaro for weight management when prescribed and monitored appropriately. Common side effects (nausea, diarrhoea) typically decrease over time. Serious side effects are rare but require immediate medical attention. Your prescriber will monitor your health throughout treatment and discuss any concerns.
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.