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 Guide for Weight Management
Mounjaro (tirzepatide) is a prescription-only weight management injection licensed in the UK for adults with obesity or overweight-related health conditions. This UK health guide explains how Mounjaro works, who is eligible, how to access it through the NHS or privately, and what to expect from this dual GLP-1 and GIP receptor agonist medication. Understanding your options is essential before discussing weight management with your GP.
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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 UK Eligibility
Mounjaro is a dual GIP and GLP-1 receptor agonist — this dual mechanism sets it apart from other weight management injections available in the UK. It works by activating two natural hormone pathways that help regulate appetite, reduce food cravings, and support feeling fuller after smaller meals. The medication also slows gastric emptying and may help your body utilise fat more effectively.
UK eligibility criteria: Adults with a BMI of 30 kg/m² or above may be eligible, or those with a BMI of 27–29.9 kg/m² if they have weight-related health conditions such as type 2 diabetes, high blood pressure, abnormal blood fats, sleep apnoea, or cardiovascular disease. For South Asian, Chinese, Black African, or Black Caribbean adults, lower BMI thresholds apply — eligibility may begin at BMI 27.5 or above due to higher health risks at lower weights. A licensed prescriber will assess your individual circumstances before prescribing.
Clinically BackedWeight Loss
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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.
Accessing Mounjaro in the UK and What to Expect
NHS access: NICE has approved tirzepatide for NHS use within specialist tier 3 and tier 4 weight management services. This means you'll need referral from your GP, and access varies significantly by region and service availability — waiting lists can be lengthy in many areas.
Private access: Available through GPhC-registered online pharmacies following an online clinical assessment with a UK-licensed prescriber. Costs typically range from £150–£300 monthly depending on dose. Clinical trials showed participants lost an average of 15–21% of body weight, though individual results vary significantly. Weight loss is most effective alongside a reduced-calorie diet and increased physical activity. Use our free BMI calculator to check your current health status and our GLP-1 weight loss calculator to explore potential outcomes at different doses.
- 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 available on the NHS in the UK?
Yes, NICE approved tirzepatide for NHS use in specialist weight management services (tier 3/4). However, you need GP referral and availability varies by region. Waiting lists can be very long. Private prescribing is also available through GPhC-registered online pharmacies without NHS referral.
What is the starting dose of Mounjaro in the UK?
The starting dose is 2.5 mg once weekly. After 4 weeks, your prescriber may increase to 5 mg, then escalate further (7.5 mg, 10 mg, 12.5 mg, 15 mg) with minimum 4-week intervals between increases, based on your response and tolerance.
What are the most common side effects of Mounjaro?
Very common side effects include nausea, diarrhoea, vomiting, constipation, and stomach pain. These often improve over time as your body adjusts. Less common but serious side effects include severe stomach pain (possible pancreatitis) and gallbladder problems — seek urgent medical attention if these occur.
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 at maximum dose, alongside diet and exercise. Individual results vary significantly — some people lose more, some less. Weight loss depends on your starting weight, adherence, diet, and physical activity level.
Can I get Mounjaro if I have type 2 diabetes?
Yes, Mounjaro is suitable for people with type 2 diabetes or prediabetes seeking weight management. In fact, having diabetes is a qualifying health condition under UK eligibility criteria. If you take insulin or other diabetes medications, your prescriber may need to adjust doses — always inform them of all medications.
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.