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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About Mounjaro — What You Need to Know
Mounjaro (tirzepatide) is a prescription-only weight management injection licensed in the UK for adults with obesity or overweight with weight-related health conditions. It's a dual GIP and GLP-1 receptor agonist, which means it works on two natural hormone pathways to help reduce appetite and support feeling fuller after meals. Unlike some other weight loss medications, Mounjaro's dual mechanism may offer a different approach to weight management. This guide explains how it works, who can access it, and what the clinical evidence shows about its potential benefits.
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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 Available Doses
Mounjaro activates two hormone pathways — GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) — which work together to regulate appetite and support weight loss. This dual action helps reduce food cravings, promotes feeling full after smaller meals, and slows how quickly food leaves the stomach. The medication comes as a pre-filled KwikPen for once-weekly injection.
Treatment starts with a 2.5 mg dose, increased gradually every 4 weeks up to a maximum of 15 mg weekly. The stepped dosing allows your body to adjust and helps minimise side effects. Clinical trials showed that participants on 15 mg lost an average of approximately 20.9% of their body weight over 72 weeks, alongside a reduced-calorie diet and increased physical activity. Individual results vary significantly — some people lose more, some less.
Use our free GLP-1 weight loss calculator to estimate potential weight loss at different doses based on your current weight.
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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.
UK Eligibility and How to Access Mounjaro
You may be eligible for Mounjaro in the UK if you have a BMI of 30 or above, or a BMI of 27–29.9 with at least one weight-related health condition such as type 2 diabetes, high blood pressure, or sleep apnoea. 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.
Mounjaro is available through NHS specialist weight management services (tier 3) or private prescribing via GPhC-registered online pharmacies. NHS access involves GP referral and can have significant waiting times depending on your region. Check your personal BMI and eligibility using our free BMI calculator — then discuss options with your GP or a licensed 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 Mounjaro the same as Wegovy?
No. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, while Wegovy (semaglutide) is a GLP-1 agonist only. Both are UK-licensed for weight management, but they work slightly differently. Clinical trials showed Mounjaro may produce slightly higher average weight loss, but individual results vary. Your prescriber will assess which is most suitable for you.
What are the most common side effects of Mounjaro?
The most common side effects are nausea, diarrhoea, vomiting, constipation, and stomach pain — these typically reduce over time as your body adjusts. Most people experience only mild symptoms. Serious side effects are rare but include severe stomach pain (possible pancreatitis) and allergic reactions. Always inform your prescriber of any persistent or concerning symptoms.
Can I get Mounjaro on the NHS in the UK?
Yes, NICE has approved tirzepatide (Mounjaro) for NHS use through specialist tier 3 weight management services. You'll need a GP referral. However, availability and waiting times vary significantly by region and ICB. Private access via online prescribing is also available without NHS referral, though this involves cost.
How long do I stay on Mounjaro?
Duration depends on your individual response and health goals. Some people use it long-term, while others use it for a defined period to achieve weight loss, then maintain with lifestyle changes. Your prescriber will discuss this with you. Stopping Mounjaro may result in weight regain, so sustained lifestyle changes are important.
Does Mounjaro work better than diet and exercise alone?
Mounjaro is designed to be used alongside a reduced-calorie diet and increased physical activity — not instead of them. Clinical trials showed that weight loss with Mounjaro occurred only when combined with these lifestyle changes. The medication helps by reducing appetite and cravings, making it easier to stick to healthier habits.
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.