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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Mounjaro Information — Everything You Need to Know
Mounjaro is a prescription-only weight management injection now available in the UK for adults living with obesity or overweight with related health conditions. 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 guide covers how Mounjaro works, who can access it, eligibility criteria, doses, expected outcomes based on clinical trials, potential side effects, and how to get it through the NHS or privately. Whether you're considering Mounjaro or want to understand more about this medication, this page has the facts you need.
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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 Mounjaro Works and Why It's Different
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — this dual-action mechanism is what sets it apart from older weight loss injections like Wegovy (semaglutide), which work on GLP-1 alone.
- GIP activation: Glucose-dependent insulinotropic polypeptide helps regulate blood sugar and appetite signals
- GLP-1 activation: Glucagon-like peptide-1 reduces appetite, increases feelings of fullness, and slows how quickly food leaves the stomach
- Combined effect: The dual mechanism may support greater appetite control and weight loss compared to single-action medications
Mounjaro is given as a once-weekly injection using a KwikPen device. It's not insulin and doesn't work the same way insulin does — even though it's injected, it's a separate weight management medication. In clinical trials (SURMOUNT-1), participants taking the maximum 15mg dose lost an average of approximately 20.9% of their body weight over 72 weeks, alongside a reduced-calorie diet and increased physical activity. However, individual results vary significantly.
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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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Mounjaro Eligibility, Doses, and UK Access
In the UK, you may be eligible for Mounjaro if you have a BMI of 30 or above, or a BMI of 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, abnormal blood fats, sleep apnoea, or cardiovascular disease. Lower BMI thresholds (BMI 27.5+) may apply if you're of South Asian, Chinese, Black African, or Black Caribbean heritage, as these groups face higher health risks at lower BMI levels. Mounjaro doses start at 2.5mg and increase gradually to a maximum of 15mg once weekly. Access through the NHS is via specialist tier 3 weight management services — waiting times vary by region. Private access is available through UK-licensed prescribers following an online clinical assessment. Use our free BMI calculator to check your BMI category and understand whether you might meet eligibility criteria for prescription weight loss treatment.
- 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's the difference between Mounjaro and Wegovy?
Both are injectable weight loss medications available in the UK, but Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, while Wegovy (semaglutide) is a single GLP-1 agonist. The dual mechanism in Mounjaro may offer greater appetite control. Clinical trial data showed Mounjaro at 15mg achieved approximately clinically studied weight loss, while Wegovy at 2.4mg achieved approximately clinically studied weight loss. Individual results vary significantly, and either medication may be suitable depending on your personal health profile.
Can I get Mounjaro on the NHS in the UK?
Mounjaro is available through NHS specialist weight management services (tier 3). NICE has approved tirzepatide for NHS use, but access varies significantly by region and NHS ICB (integrated care board). Waiting times can be several months to over a year depending on your area. Your GP can refer you to your local specialist weight management service. Private access through UK-licensed prescribers is typically faster and available without NHS referral.
What are the most common Mounjaro side effects?
The most common side effects are nausea, diarrhoea, vomiting, constipation, and stomach pain — especially when starting or increasing doses. These often improve over time as your body adjusts. Indigestion, fatigue, dizziness, injection site reactions, and hair loss are also reported. Serious side effects are rare but include severe stomach pain (possible pancreatitis) and allergic reactions. Always report persistent side effects to your prescriber.
How long do I need to take Mounjaro?
Mounjaro is typically a long-term treatment. Many people continue it for as long as it's helping them lose weight and manage their health. If you stop taking Mounjaro, weight regain is possible. Your prescriber will review whether treatment should continue based on your progress and health. Weight loss maintenance requires ongoing lifestyle changes (diet and physical activity) whether you continue medication or not.
Is Mounjaro the same as the medication used for type 2 diabetes?
Mounjaro is specifically licensed and dosed for weight management (up to 15mg once weekly). At lower doses, tirzepatide is also used to treat type 2 diabetes (where it's called Mounjaro Diabetes). The weight management version is a higher dose and distinct indication. Never use diabetes-dosed tirzepatide for weight management — dosing must match your individual prescription and clinical indication.
Ready to take control of your weight loss journey?
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