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
Free tracker included with every download this week
What Is Mounjaro Injection? A Complete NHS and UK Guide
Mounjaro is a prescription-only weekly weight loss injection licensed in the UK for adults with obesity or overweight with weight-related health conditions. It contains tirzepatide, a dual GIP and GLP-1 receptor agonist manufactured by Eli Lilly. Unlike single-action medications, Mounjaro works on two natural hormone pathways to help regulate appetite and support feeling fuller after meals. In the UK, it's available through both NHS specialist weight management services and private prescribing routes following clinical assessment. Understanding how Mounjaro works, who's eligible, and what the NHS process involves helps you make informed decisions about weight management options.
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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 NHS Eligibility Criteria
Mounjaro is a GIP and GLP-1 receptor agonist — meaning it activates two natural hormone pathways in your body. GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) are hormones that help regulate appetite, support insulin function, and slow how quickly food leaves your stomach. This dual action may help you feel fuller sooner and reduce cravings more effectively than single-action weight loss medications.
NHS eligibility for Mounjaro requires:
- 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, high blood pressure, abnormal blood fats, obstructive sleep apnoea, or a history of heart attack or stroke
- For adults of South Asian, Chinese, Black African, or Black Caribbean backgrounds, lower thresholds apply — eligibility may start at BMI 27.5 or above due to higher health risks at lower BMI levels
Your GP can assess whether you meet these criteria and refer you to a tier 3 specialist weight management service if appropriate. Use our free BMI calculator above to check your personal BMI instantly and understand your weight category according to NHS guidelines.
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.
NICE Approval, MHRA Status, and Accessing Mounjaro in the UK
Mounjaro (tirzepatide) has been approved by NICE for use within NHS specialist tier 3 and tier 4 weight management services. It carries MHRA additional monitoring status (Black Triangle ▼), meaning it's monitored closely for safety. NHS access is through specialist services only — not routine GP prescription — and availability varies significantly by region and ICB (Integrated Care Board). Waiting lists for NHS specialist weight management services can extend to many months in some areas.
Private prescribing access is available through GPhC-registered online pharmacies following a clinical assessment with a UK-licensed prescriber, without NHS referral. Both routes require a prescription from a qualified healthcare professional. Try our GLP-1 weight loss calculator to estimate potential weight loss outcomes at different Mounjaro 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 has approved Mounjaro for NHS use within specialist tier 3 and tier 4 weight management services. However, access is not through routine GP prescription — you'll need referral to a specialist service. Availability and waiting times vary significantly by region, and some areas have lengthy waiting lists.
What's the difference between Mounjaro and Wegovy?
Both are weekly weight loss injections, but they work differently. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist activating two hormone pathways. Wegovy (semaglutide) is a GLP-1-only agonist. Clinical trials suggest Mounjaro may produce slightly higher average weight loss, but individual results vary significantly. Your prescriber will assess which is more suitable for you.
How much weight can you lose with Mounjaro?
Clinical trial data (SURMOUNT-1) showed average weight loss of approximately 15–21% of body weight over 72 weeks at maximum dose, alongside a reduced-calorie diet and increased physical activity. However, results vary considerably between individuals. Some people lose more, others less — this depends on your metabolism, adherence, lifestyle changes, and overall health.
What are the main side effects of Mounjaro?
Very common side effects include nausea, diarrhoea, vomiting, constipation, and stomach pain — typically reducing as your body adjusts. Less common side effects include indigestion, acid reflux, injection site reactions, fatigue, dizziness, and hair loss. Serious side effects are rare but include severe abdominal pain (possible pancreatitis) and allergic reactions — seek immediate medical attention if these occur.
Can I get Mounjaro privately in the UK if I'm not eligible for NHS?
Yes, private prescribing is available through GPhC-registered online pharmacies following a clinical assessment. You don't need NHS referral, but you do need a prescription from a UK-licensed prescriber. They'll assess your suitability based on your health history, BMI, and any weight-related conditions. Costs vary by dose and provider but typically range from £129–£320 monthly.
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.