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 — Complete UK Health Information Guide
Mounjaro (tirzepatide) is a prescription-only weight management injection licensed in the UK for adults with obesity or overweight with health conditions. It works differently from other weight loss medications by activating two natural hormone pathways — GIP and GLP-1 — which may help reduce appetite and support weight loss alongside diet and physical activity. Understanding how Mounjaro works, who is eligible, and what to expect can help you make informed decisions about your health with your GP or a licensed prescriber.
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Calculate Your BMI Instantly
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 What It Does
Mounjaro is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways that regulate hunger and blood sugar. This dual action may help you feel fuller after smaller meals, reduce cravings, and support weight loss when combined with a reduced-calorie diet and increased physical activity.
The medication is injected once weekly under the skin using a pre-filled KwikPen. It is not insulin and works differently from diabetes medications, though it can also help with blood sugar control in people with type 2 diabetes or prediabetes.
In clinical trials (SURMOUNT-1), participants taking Mounjaro alongside lifestyle changes lost an average of 15–21% of their body weight over 72 weeks, depending on the dose. However, individual results vary significantly — some people lose more, some less. Weight loss is not assured, and it requires commitment to dietary and lifestyle changes.
You can use our free GLP-1 weight loss calculator above to estimate potential weight loss at different Mounjaro doses based on your starting weight.
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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 Eligibility, Doses, and How to Access Mounjaro
You may be eligible for Mounjaro in the UK if you have a BMI of 30 or above, or a BMI of 27–29.9 with at least one weight-related health condition (type 2 diabetes, prediabetes, high blood pressure, high cholesterol, sleep apnoea, or cardiovascular disease). If you are of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds may apply.
Mounjaro is available on the NHS through specialist tier 3/4 weight management services (often with waiting lists), or privately through a licensed prescriber following an online clinical assessment. Doses start at 2.5 mg weekly and increase gradually up to a maximum of 15 mg.
Common side effects include nausea, diarrhoea, and constipation, particularly at the start — these often improve over time. Check your BMI using our free calculator above to understand where you sit on the NHS healthy weight scale and discuss Mounjaro eligibility with your GP.
- 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?
No. Both contain tirzepatide's cousin semaglutide, but Ozempic (up to 2 mg) is licensed for type 2 diabetes, while Mounjaro (up to 15 mg) is licensed specifically for weight management. Mounjaro is a newer medication with a dual GIP+GLP-1 mechanism, whereas other GLP-1 medications like Wegovy activate only the GLP-1 pathway.
How much weight can I expect to lose with Mounjaro?
Clinical trials showed average weight loss of 15–21% of body weight over 72 weeks, but results vary widely. Some people lose more, some less. Weight loss depends on the dose, your starting weight, diet adherence, activity level, and individual metabolism. Your prescriber can discuss realistic expectations for you personally.
Can I get Mounjaro on the NHS in the UK?
Mounjaro is approved by NICE for NHS specialist weight management services (tier 3/4). However, NHS access varies significantly by region and waiting lists can be very long. Private access is available through licensed prescribers without an NHS referral, though this involves a cost.
What are the most common side effects of Mounjaro?
Very common side effects include nausea, diarrhoea, vomiting, constipation, and stomach pain — particularly in the first few weeks. These often improve as your body adjusts. Less common side effects include headache, fatigue, dizziness, and injection site reactions. Seek urgent medical attention for severe persistent stomach pain.
How often do I inject Mounjaro and can I store it at home?
Mounjaro is a once-weekly injection given under the skin on the same day each week. Each pre-filled KwikPen contains 4 doses (4 weeks' supply). Unopened pens are stored in a fridge at 2–8°C. After first use, pens can be kept at room temperature (below 30°C) for up to 30 days before disposal.
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.