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 Injection in the UK — Complete Information Guide
Mounjaro (tirzepatide) is a prescription-only, once-weekly weight loss injection licensed in the UK for adults with excess weight and weight-related 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 feelings of fullness. Access in the UK is available through NHS specialist weight management services or via private online prescribing following a clinical assessment. This guide explains how Mounjaro works, UK eligibility criteria, doses, and what to expect.
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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 UK Eligibility
Mechanism: Mounjaro is a dual GIP and GLP-1 receptor agonist, which means it activates two natural hormone pathways in your body. This dual action may help regulate appetite, reduce food cravings, and support feeling fuller after smaller meals. It also slows how quickly food leaves your stomach, though this effect typically reduces over time.
- GIP receptor activation: Helps regulate fat utilisation and appetite signals
- GLP-1 receptor activation: Reduces hunger and supports blood sugar control
UK eligibility for Mounjaro: You may be eligible if you have a BMI of 30 kg/m² or above, or a BMI of 27–29.9 kg/m² with at least one weight-related health condition (such as type 2 diabetes, prediabetes, high blood pressure, abnormal blood fats, sleep apnoea, or cardiovascular disease). If you're of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds may apply. A prescriber will assess your individual health during a clinical 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.
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Mounjaro Doses, Side Effects, and UK Access
Dosing schedule: Mounjaro starts at 2.5 mg weekly and can be increased gradually to a maximum of 15 mg per week, based on your response and tolerance. Each KwikPen contains four weekly doses. Clinical trials (SURMOUNT-1) showed average weight loss of approximately 15–21% of body weight over 72 weeks alongside a reduced-calorie diet and increased physical activity — though individual results vary significantly.
Common side effects include nausea, diarrhoea, vomiting, constipation, and stomach pain, especially when starting or increasing doses. Most side effects improve over time. Seek urgent medical attention for severe, persistent stomach pain (possible pancreatitis), serious allergic reactions, or gallbladder problems.
UK access: Mounjaro is available through NHS tier 3 specialist weight management services (via GP referral, though availability and waiting times vary) or through private online prescribing with a UK-licensed prescriber, dispensed by a GPhC-registered pharmacy.
- 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 Wegovy?
No. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, while Wegovy (semaglutide) is a GLP-1-only agonist. Both are once-weekly injections licensed for weight loss in the UK, but they have different mechanisms. Clinical trials show Mounjaro may produce slightly higher average weight loss, though results vary between individuals. Your prescriber will advise which is most suitable for you.
How quickly will I lose weight on Mounjaro?
Weight loss happens gradually. The NHS recommends aiming for approximately 0.5–1 kg per week. In the SURMOUNT trial, participants on Mounjaro lost an average of 15–21% of their body weight over 72 weeks, alongside dietary and lifestyle changes. Individual results vary considerably based on adherence, diet, and activity level. Try our GLP-1 weight loss calculator to see projected outcomes at different doses.
Can I get Mounjaro on the NHS in the UK?
Yes, but access varies significantly by region. NICE has approved tirzepatide for NHS use within specialist tier 3 weight management services. You'll need a GP referral and assessment. However, waiting lists can be months or years in many areas. Private access via online prescribing is often faster but involves private costs, typically £150–£300 per month depending on dose.
What happens if I miss a Mounjaro injection?
If you miss a dose, take it within 4 days of the scheduled day and continue your normal weekly schedule. If more than 4 days have passed, skip that dose and take your next dose on the normally scheduled day. Never take a double dose. Maintain at least 72 hours between injections. Contact your prescriber if you're unsure.
Does Mounjaro work without diet and exercise changes?
Mounjaro may help reduce appetite and support weight loss, but clinical trials show best results when combined with a reduced-calorie diet and increased physical activity. It is a tool to support lifestyle change, not a replacement for it. Your GP or prescriber will discuss realistic expectations and how to integrate Mounjaro with dietary and exercise modifications for sustainable results.
Ready to take control of your weight loss journey?
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