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 and How Does It Work?
Mounjaro is a prescription-only weight management injection containing tirzepatide, approved for use in the UK. It works differently from other weight loss injections because it activates two natural hormone pathways — GIP and GLP-1 — rather than just one. This dual action may help regulate appetite, reduce food cravings, and support feeling fuller after meals. Mounjaro is administered as a once-weekly injection and requires a clinical assessment before prescription. Results vary between individuals, and it's used alongside a reduced-calorie diet and increased physical activity.
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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 Eligibility in the UK
Mechanism of action: Mounjaro (tirzepatide) activates both GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) receptors. This dual mechanism may help your body regulate appetite more effectively than single-pathway medications. It slows how quickly food leaves your stomach and helps regulate fat utilisation.
- You may feel fuller after eating smaller portions
- Food cravings may reduce, particularly for sweet or fatty foods
- The medication is not insulin and does not work in the same way as diabetes injections
UK eligibility: You may be eligible for Mounjaro if you have a BMI of 30 kg/m² or above, or a BMI of 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. Lower thresholds apply for South Asian, Chinese, Black African, and Black Caribbean adults. Use our free BMI calculator above to check your personal BMI instantly.
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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 Doses, Side Effects, and Getting It in the UK
Doses and treatment: Mounjaro starts at 2.5 mg once weekly and may be increased every 4 weeks up to a maximum of 15 mg. Clinical trials (SURMOUNT-1) showed participants lost an average of 15–21% of their body weight over 72 weeks — though individual results vary significantly. Each KwikPen contains 4 doses.
Common side effects: Nausea, diarrhoea, vomiting, and constipation are very common, especially when starting or increasing doses. Stomach pain, indigestion, injection site reactions, and fatigue may also occur. Side effects typically improve as your body adjusts. Seek urgent medical attention if you experience severe stomach pain spreading to your back (possible pancreatitis).
Getting Mounjaro in the UK: NHS access is through specialist tier 3 weight management services — waiting lists vary by region. Private access is available through GPhC-registered online pharmacies following an online clinical assessment. Try our GLP-1 weight loss calculator to explore potential outcomes at different 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 the same as Ozempic?
No. Both contain semaglutide, but Ozempic is approved for type 2 diabetes (not weight loss in the UK). Mounjaro contains tirzepatide and is a dual GIP+GLP-1 agonist, whereas Wegovy (also semaglutide) is a single GLP-1 agonist. Mounjaro and Wegovy are the UK-licensed weight management options.
How much weight will I lose on Mounjaro?
Clinical trials showed an average weight loss of 15–21% of body weight over 72 weeks, but individual results vary considerably. Some people lose more, some less. Weight loss depends on dose, adherence, diet, physical activity, and personal metabolism. Your prescriber can discuss realistic expectations for your situation.
Can I get Mounjaro on the NHS?
Yes, but access is through specialist tier 3 weight management services, not standard GP prescription. You'll need referral from your GP. Waiting times vary significantly by region — some areas have very long waiting lists. Private access is available without NHS referral.
What happens if I stop taking Mounjaro?
Weight typically returns over time once treatment stops, especially if lifestyle changes aren't maintained. Mounjaro is not a permanent solution — it's a tool to support weight loss alongside diet and exercise. Your prescriber will discuss long-term management when treatment ends.
Is Mounjaro safe for type 2 diabetes?
Mounjaro is approved for weight management in adults with or without type 2 diabetes. If you have diabetes and take insulin or certain diabetes medications, your doses may need adjustment. Always inform your prescriber of all medications — they'll assess safety and manage any interactions.
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.