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 Moanjaro? A Complete UK Health Guide
Moanjaro (tirzepatide) is a prescription-only weight management injection licensed in the UK for adults with obesity or overweight and weight-related health conditions. Unlike some other weight loss medications, Moanjaro works via a dual mechanism — activating both GIP and GLP-1 hormone pathways — which may help reduce appetite and support sustainable weight management. This guide covers how Moanjaro works, UK eligibility criteria, dosing, expected outcomes from clinical trials, and important safety information to help you understand this nhs health advice context and make informed decisions with your GP.
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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 Moanjaro Works and What Makes It Different
Moanjaro is a dual GIP and GLP-1 receptor agonist, which sets it apart from single-mechanism weight loss medications. It activates two natural hormone pathways in your body: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1). This dual action may help regulate appetite more effectively, reduce food cravings, and support feeling fuller after smaller meals. The medication also slows how quickly food leaves your stomach, though this effect typically reduces over time. Moanjaro is not insulin — it works through hormone signalling, not by directly managing blood sugar in the way insulin does. It's administered as a once-weekly injection using a pre-filled KwikPen device. Clinical trials (SURMOUNT-1) showed that on average, participants lost approximately 15–21% of their body weight alongside a reduced-calorie diet and increased physical activity, though individual results vary significantly. Try our GLP-1 weight loss calculator to estimate potential outcomes at different doses.
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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.
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UK Eligibility and How to Access Moanjaro
In the UK, Moanjaro may be prescribed for adults with a BMI of 30 kg/m² or above (obesity), or BMI of 27–29.9 kg/m² (overweight) if you have at least one weight-related health condition such as type 2 diabetes, prediabetes, high blood pressure, abnormal blood fats, obstructive sleep apnoea, or cardiovascular disease history. For people of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds may apply due to higher health risks at lower weights. Check your BMI using our free BMI calculator above. Access routes vary: NHS specialist weight management services can prescribe Moanjaro following referral, though waiting lists vary by region. Private UK-licensed prescribers can assess and prescribe following an online consultation. Moanjaro is prescription-only and requires clinical assessment before dispensing — it cannot be purchased without a valid prescription from a UK-licensed healthcare professional.
- 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.
What is the starting dose of Moanjaro, and how does it increase?
Moanjaro starts at 2.5 mg once weekly for the first 4 weeks. The dose then increases in steps — typically to 5 mg, then 7.5 mg, 10 mg, 12.5 mg, and up to a maximum of 15 mg weekly. Each dose is held for at least 4 weeks before increasing, allowing your body to adjust. Your prescriber will determine the right dose progression for you based on your response and tolerability.
How much weight can you typically lose with Moanjaro?
Clinical trial data (SURMOUNT-1) showed that participants lost on average 15–21% of their body weight at 72 weeks, depending on dose and alongside lifestyle changes. However, individual results vary significantly — some people lose more, some less. Weight loss is not assured, and results depend on adherence to reduced-calorie diet and increased physical activity alongside the medication.
What are the most common side effects of Moanjaro?
The most common side effects are nausea, diarrhoea, vomiting, constipation, and stomach pain — affecting more than 1 in 10 people. These often improve over time as your body adjusts. Other common effects include indigestion, fatigue, dizziness, and injection site reactions. Serious side effects are rare but can include severe stomach pain (possible pancreatitis) or gallbladder problems — seek immediate medical attention if these occur.
Can I switch between Moanjaro and Wegovy?
Both are prescription-only weight management injections licensed in the UK, but switching requires prescriber guidance. Moanjaro is a dual GIP/GLP-1 agonist, while Wegovy (semaglutide) is a GLP-1 agonist only — they have different mechanisms and doses are not directly equivalent. Any switch must be managed by your healthcare professional based on your individual response and health status.
Is Moanjaro available on the NHS?
Yes — NICE has approved tirzepatide (Moanjaro) for use within NHS specialist weight management services. Access is through tier 3/4 services, typically following GP referral, and varies significantly by region and local ICB (Integrated Care Board) availability. Many areas have substantial waiting lists. Private prescription access is available through UK-licensed online prescribers without NHS referral, though this involves private costs.
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.