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 — UK Health Information Guide
Mounjaro (tirzepatide) is a prescription-only, once-weekly injectable medicine licensed in the UK for weight management in adults. It works differently to other weight loss injections because it activates two natural hormone pathways — GIP and GLP-1 — which may help reduce appetite and support feeling fuller after meals. This UK health guide explains how Mounjaro works, who may be eligible, what to expect, and where to access it through the NHS or private prescribing. Always consult your GP or a qualified healthcare professional before considering any weight management treatment.
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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 Eligibility in the UK
Mounjaro is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways in your body. This dual action may help regulate appetite, reduce food cravings, and support you feeling satisfied after smaller meals. It also slows how quickly food leaves your stomach, though this effect typically reduces over time. The medicine is not insulin and works in a completely different way.
UK eligibility criteria:
- BMI of 30 kg/m² or above (obesity), OR
- BMI of 27–29.9 kg/m² (overweight) with at least one weight-related health condition such as type 2 diabetes, high blood pressure, or sleep apnoea
- Lower thresholds may apply for South Asian, Chinese, Black African, or Black Caribbean adults — starting from BMI 27.5 or above
- Must be 18 years or older
- Cannot be pregnant, breastfeeding, or planning pregnancy
Mounjaro is prescription-only and requires a clinical assessment from a GP or licensed prescriber to confirm suitability. Use our free BMI calculator above to check your current BMI and assess where you fall on the NHS healthy weight scale.
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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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Mounjaro Doses, Weight Loss Results, and Side Effects
Mounjaro is administered as a once-weekly injection, starting at 2.5 mg and escalating up to a maximum of 15 mg depending on how your body responds. Clinical trials (SURMOUNT-1) showed that participants using Mounjaro lost an average of 15–21% of their body weight over 72 weeks — though individual results vary significantly and depend on lifestyle changes including diet and physical activity.
Common side effects include nausea, diarrhoea, vomiting, constipation, and stomach pain, particularly when starting or increasing the dose. Most side effects improve over time. Seek urgent medical attention if you experience severe, persistent stomach pain (possible pancreatitis), serious allergic reactions, or changes in vision.
Track your weight loss progress using our free progress tracker to monitor changes week-by-week. Our GLP-1 weight loss calculator can help you estimate potential results at different doses alongside healthy lifestyle changes.
- 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 semaglutide, but Ozempic is licensed for type 2 diabetes (doses up to 2 mg), while Wegovy is the licensed weight management version. Mounjaro is different — it contains tirzepatide, a dual GIP+GLP-1 agonist, and is a separate weight management medicine. Never use diabetes medications off-label for weight loss without medical supervision.
How do I get Mounjaro on the NHS in the UK?
Mounjaro is available through NHS tier 3 specialist weight management services. You'll need a referral from your GP, followed by assessment by a specialist team. Availability and waiting times vary significantly by region. Private access is also available through GPhC-registered pharmacies following an online clinical assessment with a UK-licensed prescriber.
What is the difference between Mounjaro and Wegovy?
Both are once-weekly weight loss injections, but Mounjaro (tirzepatide) is a dual GIP+GLP-1 agonist, while Wegovy (semaglutide) is a GLP-1-only agonist. Clinical trials suggest Mounjaro may produce slightly higher average weight loss (15–21% vs ~15%), though results vary individually. Your prescriber will assess which is more appropriate for your health.
What happens if I miss a Mounjaro injection?
If you miss a dose, take it within 4 days of the scheduled date and continue your normal weekly schedule. If more than 4 days have passed, skip that dose and take your next one on the usual day. Never double-dose. Ensure at least 72 hours (3 days) between injections.
Can I take Mounjaro if I'm on other medications?
Mounjaro may affect how your body absorbs oral medications, particularly oral contraceptives — additional contraception should be used for 4 weeks after starting and after each dose increase. If you take diabetes medications, your prescriber may need to adjust doses. Always tell your GP or prescriber about all medications you take before starting Mounjaro.
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.