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 Maunjaro? UK Health Guide
Maunjaro (tirzepatide) is a prescription-only, once-weekly injectable medication licensed in the UK for weight management in adults. 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 mechanism may help regulate appetite, reduce cravings, and support feeling fuller after smaller meals. Maunjaro is manufactured by Eli Lilly and available through NHS specialist weight management services or private online prescribing following a clinical assessment. This guide covers how Maunjaro works, UK eligibility criteria, available doses, and what the research shows about expected outcomes.
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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 Maunjaro Works and UK Eligibility
Mechanism of action: Maunjaro is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways that regulate appetite and blood sugar. This dual action may be more effective than single-mechanism injections for some people. It helps reduce hunger signals, slows gastric emptying (how quickly food leaves the stomach), and may support sustainable weight loss alongside a reduced-calorie diet and increased physical activity.
UK eligibility criteria: You may be eligible for Maunjaro if you have a BMI of 30 kg/m² or above, or a BMI of 27–29.9 kg/m² with at least one weight-related health condition such as type 2 diabetes, high blood pressure, abnormal blood fats, sleep apnoea, or cardiovascular disease. If you're of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds may apply (from BMI 27.5). Age 18 and over only. Pregnancy, breastfeeding, or allergy to tirzepatide are contraindications. A prescriber will assess your individual suitability during a clinical consultation using our healthy weight UK guidelines and NHS criteria.
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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.
Maunjaro Doses, Side Effects, and Weight Loss Results
Dosing schedule: Maunjaro starts at 2.5 mg once weekly, with doses escalating by 2.5 mg every four weeks as tolerated, up to a maximum of 15 mg weekly. Each pen contains four doses (one month's supply) and is stored in the fridge at 2–8°C. You'll inject under the skin on your stomach, thigh, or upper arm, rotating sites each week.
Clinical results: In the SURMOUNT-1 trial, participants on Maunjaro 15 mg lost an average of around 20.9% of their body weight over 72 weeks, alongside diet and exercise. However, individual results vary significantly — some people lose more, some less. Common side effects include nausea, diarrhoea, constipation, and stomach discomfort, usually mild and temporary. Try our GLP-1 weight loss calculator to estimate 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 Maunjaro the same as Wegovy?
No. Maunjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, while Wegovy (semaglutide) is a GLP-1 agonist only. Both are prescription-only weight management injections licensed in the UK, but they work via different mechanisms. Clinical trials show slightly different average weight loss outcomes, though individual results vary. Your prescriber will assess which is more suitable for your circumstances.
How do I access Maunjaro in the UK?
Through two routes: NHS specialist tier 3 weight management services (referral from your GP, though availability and waiting times vary significantly by region) or private online prescribing through a GPhC-registered pharmacy following an online clinical assessment. Private access typically costs £129–£320 per month depending on dose. Either route requires a prescription from a UK-licensed prescriber.
What's the difference between Maunjaro and Ozempic?
Both contain the same active ingredient (semaglutide), but Ozempic is approved for type 2 diabetes (up to 2 mg doses) and is not licensed for weight loss in the UK. Maunjaro is tirzepatide, a different medication entirely. If you see "Ozempic for weight loss" mentioned, that's off-label use — Maunjaro or Wegovy are the licensed weight management options.
How quickly will I lose weight on Maunjaro?
Weight loss typically becomes noticeable after 4–8 weeks as your dose builds up. The NHS recommends a safe rate of 0.5–1 kg per week. Clinical trials showed an average loss of 15–21% of body weight over several months, but this varies based on your starting weight, diet, exercise, and how your body responds. Use our BMI calculator to track your progress from your starting point.
What are the most common side effects?
Nausea, diarrhoea, vomiting, constipation, and stomach pain are very common, especially in the first few weeks. These usually improve as your body adjusts. Less common side effects include headache, fatigue, dizziness, and injection site reactions. Serious side effects are rare but include severe stomach pain (pancreatitis) or gallbladder problems — seek medical attention immediately if these occur.
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.