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 Guidelines for UK Adults
Mounjaro (tirzepatide) is a prescription-only weight management injection now available in the UK through both NHS specialist services and private prescription. This guide explains the clinical guidelines, eligibility criteria, dosing schedules, and what to expect when using this dual GIP and GLP-1 receptor agonist. Understanding the guidelines helps you have an informed conversation with your GP or prescriber about whether Mounjaro is right for your health goals.
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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.
UK Eligibility and Access Guidelines
NICE Guidance and NHS Access: The National Institute for Health and Care Excellence (NICE) has approved tirzepatide (Mounjaro) for use within NHS specialist weight management services for adults meeting specific 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, prediabetes, hypertension, dyslipidaemia, obstructive sleep apnoea, or cardiovascular disease history
- For South Asian, Chinese, Black African, and Black Caribbean adults, lower thresholds apply: BMI of 27.5 or above may qualify due to higher metabolic risk at lower BMI levels
Access is through tier 3 specialist weight management services, which requires referral from your GP. Waiting times vary significantly by region (ICB). Private prescription is available through UK-licensed prescribers without NHS referral. Use our free BMI calculator above to check your personal BMI and understand where you stand relative to these guidelines.
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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.
Mounjaro Dosing and Titration Guidelines
Standard Dose Titration Schedule: Mounjaro is injected once weekly, starting at 2.5 mg and increasing every 4 weeks if tolerated. The maximum dose is 15 mg weekly. Each KwikPen contains 4 weekly doses (4-week supply).
- Weeks 1–4: 2.5 mg (starting dose)
- Weeks 5–8: 5 mg (first maintenance option)
- Weeks 9–12: 7.5 mg, Weeks 13–16: 10 mg (escalation as needed)
- Weeks 17–20: 12.5 mg, Week 21+: 15 mg (maximum dose)
Dosing is individualised — some patients benefit from staying at a lower dose, whilst others reach the full 15 mg dose. Your prescriber will guide titration based on your response and tolerability. Our GLP-1 weight loss calculator can help you explore projected outcomes at different dose levels alongside 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.
What is the difference between Mounjaro and Wegovy?
Both are prescription-only weight management injections licensed in the UK. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist with a maximum dose of 15 mg weekly, whilst Wegovy (semaglutide) is a GLP-1 agonist only with a maximum dose of 2.4 mg weekly. Clinical trials show similar average weight loss (~15–21% for Mounjaro, ~15% for Wegovy), but individual results vary. Your prescriber will discuss which is most suitable.
Can I access Mounjaro through the NHS?
Yes, Mounjaro is available through NHS specialist tier 3 weight management services following NICE approval. However, access varies significantly by region and waiting lists can be long. Your GP can refer you to your local specialist service. Private prescription is an alternative option if you wish to access Mounjaro sooner without waiting for NHS assessment.
What are the most common side effects of Mounjaro?
The most common side effects are gastrointestinal: nausea, diarrhoea, vomiting, and constipation. These often improve as your body adjusts over weeks or months. Less common side effects include stomach pain, indigestion, fatigue, dizziness, and injection site reactions. Serious side effects are rare but include severe stomach pain (possible pancreatitis) and gallbladder problems — seek immediate medical attention if these occur.
Do I need to follow a diet and exercise plan whilst taking Mounjaro?
Yes. Mounjaro is most effective when combined with a reduced-calorie diet and increased physical activity. The medication helps you feel fuller and reduces cravings, but sustainable weight loss requires consistent lifestyle changes. A balanced Mediterranean-style diet and 150 minutes of moderate activity per week are recommended by NHS guidelines. Track your progress using our free progress tracker.
How long do I stay on Mounjaro?
Duration depends on your individual health and weight loss goals. Some people use it for a defined period (e.g., 1–2 years) to achieve target weight, then transition to lifestyle maintenance. Others use it long-term if weight regain occurs or health conditions require ongoing management. This decision is made with your prescriber based on your response, tolerability, and personal goals.
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.