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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What Is Monjaru? A UK Health Guide
Monjaru (tirzepatide) is a prescription-only weight management injection licensed in the UK for adults with excess weight. It's a dual GIP and GLP-1 receptor agonist, meaning it works on two natural hormone pathways to help regulate appetite and support feeling fuller after meals. This NHS guidance-aligned information will help you understand how Monjaru works, who can access it, and what results clinical trials have shown. Always consult your GP or a licensed prescriber before considering any weight management treatment.
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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 Monjaru Works and What It Does
Monjaru activates two hormone pathways — GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) — which is what distinguishes it from other weight management injections like Wegovy (semaglutide). This dual mechanism may help reduce appetite, decrease food cravings, and support feeling fuller after smaller meals. Monjaru also slows gastric emptying, meaning food passes through your stomach more gradually, though this effect typically reduces over time. It helps your body regulate fat utilisation more effectively. In the SURMOUNT-1 clinical trial, participants taking the maximum dose (15 mg once weekly) lost an average of approximately 20.9% of their body weight over 72 weeks. Results varied significantly between individuals — some lost more, some less. Weight loss was achieved alongside a reduced-calorie diet and increased physical activity, not instead of these lifestyle changes. Calculate your current BMI and explore potential outcomes using our free BMI calculator and GLP-1 weight loss calculator on this page.
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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.
UK Eligibility, Doses, and How to Access Monjaru
In the UK, Monjaru may be prescribed to adults with a BMI of 30 kg/m² or above, or 25–29.9 kg/m² with at least one weight-related health condition (such as type 2 diabetes, high blood pressure, or cardiovascular disease). South Asian, Chinese, Black African, and Black Caribbean adults may qualify at lower BMI thresholds (from BMI 27.5) due to higher health risks at these levels — this is NHS guidance. Monjaru is available as a once-weekly injection at doses ranging from 2.5 mg (starting dose) to 15 mg (maximum). Access in the UK is via NHS specialist weight management services or through private prescribing following an online clinical assessment. Your prescriber will assess whether Monjaru is suitable for your individual health profile. Use our free weight converter and progress tracker to monitor your weight in kg, stone, and pounds throughout your journey.
- 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 Monjaru the same as Wegovy?
No. Monjaru (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 management in the UK. Clinical trials showed Monjaru resulted in slightly higher average weight loss (~21% vs ~15%), but individual results vary. Your prescriber will help determine which is more suitable for you.
How much weight can I expect to lose on Monjaru?
In the SURMOUNT-1 trial, participants lost an average of 15–21% of body weight depending on dose, over 72 weeks alongside lifestyle changes. Results vary considerably — some individuals lose more, others less. Weight loss is not assured. Your GP or prescriber can discuss realistic expectations for your situation.
What are the main side effects of Monjaru?
Very common side effects include nausea, diarrhoea, vomiting, and stomach pain, especially when starting or increasing doses. These often improve over time. Less common side effects include fatigue, dizziness, and injection site reactions. Serious side effects are rare but seek urgent medical attention for severe stomach pain (possible pancreatitis) or difficulty breathing.
How do I access Monjaru in the UK?
Via NHS specialist tier 3 weight management services (requires GP referral, though waiting lists vary by region) or through private prescribing following an online clinical assessment with a UK-licensed prescriber. Both routes require a valid prescription. Private access is generally faster but involves a cost.
Can I get Monjaru on the NHS?
Yes, NICE has approved tirzepatide (Monjaru) for use within NHS specialist weight management services. However, availability depends on your local integrated care board (ICB), and waiting lists can be lengthy in many areas. Your GP can refer you to your local specialist service to check eligibility and current waiting times.
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.