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 Weight Management Guide
Mounjaro (tirzepatide) is a prescription-only weight management injection licensed in the UK for adults with obesity or overweight with weight-related health conditions. This comprehensive guide covers how Mounjaro works, who may be eligible, expected outcomes based on clinical trials, potential side effects, and how to access it through both NHS and private routes. Whether you're exploring weight management options or researching treatment eligibility, this UK health information covers the key facts you need to know.
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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 to Expect
Mounjaro is a dual GIP and GLP-1 receptor agonist — this dual mechanism sets it apart from other weight loss injections like Wegovy, which works through GLP-1 alone. Mounjaro activates two natural hormone pathways that help regulate appetite and food cravings. It may support feeling fuller after smaller meals and help reduce overall food intake.
The medication is administered as a once-weekly injection using a pre-filled KwikPen device. Treatment typically starts at 2.5 mg and increases gradually over weeks, with a maximum dose of 15 mg weekly. Each pen contains four weekly doses. Clinical trials showed participants on Mounjaro lost an average of 15–21% of their body weight over 72 weeks, though individual results vary significantly. Weight loss is most effective when combined with a reduced-calorie diet and increased physical activity.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
Eligibility and How to Access Mounjaro in the UK
UK eligibility criteria: Adults may be eligible for Mounjaro if they have a BMI of 30 or above, or BMI of 27–29.9 with at least one weight-related health condition such as type 2 diabetes, high blood pressure, or cardiovascular disease. Lower BMI thresholds may apply for people of South Asian, Chinese, Black African, or Black Caribbean heritage due to higher health risks at lower weights.
How to access: NHS access is through specialist tier 3 weight management services — typically requiring GP referral and assessment. Private access is available through UK-licensed online prescribing services following a clinical assessment. A qualified healthcare professional will evaluate your individual circumstances before prescribing. Our free BMI calculator can help you understand where you fall within NHS health guidelines.
- 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.
What is Mounjaro and how does it differ from Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist made by Eli Lilly. Wegovy (semaglutide) is a GLP-1 agonist only, made by Novo Nordisk. Both are once-weekly injections licensed for UK weight management. Clinical trials showed Mounjaro may help achieve slightly higher average weight loss than Wegovy, but individual results vary significantly. Your prescriber can advise which is more suitable for you.
Who is eligible for Mounjaro on the NHS in the UK?
NHS eligibility typically requires BMI of 30 or above, or 27–29.9 with a weight-related health condition like type 2 diabetes or high blood pressure. You usually need referral to a specialist tier 3 weight management service through your GP. Regional availability varies, and waiting lists can be lengthy. Private prescribing is available without NHS referral following online clinical assessment.
What are the most common side effects of Mounjaro?
Very common side effects include nausea, diarrhoea, constipation, vomiting, and stomach pain, particularly when starting or increasing doses. These often improve over time. Less common side effects include fatigue, dizziness, headache, and injection site reactions. Serious side effects are rare but include severe stomach pain (possible pancreatitis) or serious allergic reactions — seek immediate medical attention if these occur.
How much weight can I expect to lose on Mounjaro?
Clinical trials showed average weight loss of 15–21% of body weight over 72 weeks at the highest dose. However, individual results vary considerably — some people lose less, some lose more. Weight loss depends on starting weight, adherence to medication, diet, physical activity, and individual metabolism. Your prescriber can discuss realistic expectations for your situation. Even modest weight loss (5–10%) provides health benefits.
How do I get Mounjaro in the UK — NHS or private?
NHS: Referral to a specialist weight management service through your GP. Private: Online consultation with a UK-licensed prescriber, prescription issued if suitable, dispensed by a registered pharmacy. NHS access is free but involves referral and may have waiting lists. Private access is faster but involves costs ranging from approximately £129–£320 monthly depending on dose.
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.