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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Monjaru — What You Need to Know in the UK
Monjaru is a prescription-only weight management injection licensed in the UK for adults with obesity or excess weight. If you've heard about slimming injections or weight loss jabs, Monjaru (tirzepatide) is likely what's being discussed. This UK health guide explains how it works, who may be eligible, how to access it through the NHS or privately, and what to expect. Understanding your options for healthy weight management is an important first step — our BMI calculator can help you assess your current health status using NHS guidelines.
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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 Monjaru Works and NHS Eligibility in the UK
Monjaru contains tirzepatide, a dual GIP and GLP-1 receptor agonist — this means it activates two natural hormone pathways that help regulate appetite and food intake. Unlike some weight loss approaches, Monjaru works by helping you feel fuller after smaller meals and may reduce cravings.
In the UK, NHS guidance states you may be eligible for Monjaru if you have:
- A BMI of 30 kg/m² or above (obesity), OR
- A BMI of 27–29.9 kg/m² (overweight) with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea
- For South Asian, Chinese, Black African, or Black Caribbean adults, lower BMI thresholds may apply (from BMI 27.5)
Clinical trials showed participants lost an average of 15–21% of their body weight over 72 weeks — though individual results vary significantly. Our free GLP-1 weight loss calculator can help you estimate potential outcomes based on your current weight and starting dose.
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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.
Accessing Monjaru in the UK — NHS and Private Routes
In the UK, Monjaru access works through two main routes. Via the NHS: You'll need a referral from your GP to a specialist tier 3 weight management service. NHS availability varies by region, and waiting lists can be lengthy. Via private prescribing: You can access Monjaru through a private online consultation with a UK-licensed prescriber, without an NHS referral. A GPhC-registered pharmacy dispenses the medication following clinical assessment. Use our free BMI calculator to check where your weight sits on NHS guidance — this information is useful when discussing options with your GP or a prescriber.
- 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 available on the NHS in the UK?
Monjaru is approved by NICE for use within NHS specialist weight management services (tier 3). Access is through referral from your GP, not direct prescription. Availability and waiting times vary significantly by region and local ICB decisions. Your GP can advise whether you're eligible and how to access it in your area.
What is the difference between Monjaru and Wegovy?
Both are prescription-only weight loss injections licensed in the UK. Monjaru (tirzepatide) is a dual GIP+GLP-1 agonist; Wegovy (semaglutide) is a GLP-1 agonist only. Clinical trials showed similar average weight loss (15–21% for Monjaru, approximately 15% for Wegovy). Individual response varies. Your prescriber will assess which is more suitable for you.
What are the main side effects of Monjaru in the UK?
Very common side effects include nausea, diarrhoea, vomiting, constipation, and stomach pain — especially during dose adjustments. These often improve over time. Common side effects include indigestion, fatigue, and injection site reactions. Serious side effects are rare but include severe stomach pain (possible pancreatitis) and allergic reactions. Always report any concerns to your prescriber.
How much does Monjaru cost privately in the UK?
Private Monjaru costs typically range from £150–£320 per month depending on dose and provider. Starting doses (2.5 mg) cost less than higher doses. Each KwikPen contains 4 weekly doses. Cost varies between online prescribing services — compare providers for the best price. NHS prescription costs standard NHS prescription fees if accessed via NHS specialist services.
How long does it take to see weight loss results with Monjaru?
Most people begin noticing changes within 2–4 weeks of starting, though significant weight loss typically becomes evident after 8–12 weeks. Monjaru works best alongside a reduced-calorie diet and increased physical activity. Results vary between individuals. Track your progress over time — our free progress tracker can help you monitor changes beyond just weight, including how you feel and your energy levels.
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.