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 Mounjro?
Mounjro is a prescription-only weight management injection available in the UK. It contains tirzepatide, a medication that works by activating two natural hormone pathways to help reduce appetite and support weight loss alongside diet and exercise. If you're exploring weight management options, it's important to understand how this medication works and whether it might be suitable for you following a clinical assessment by a healthcare professional.
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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 Mounjro Works in Your Body
Mounjro is a dual GIP and GLP-1 receptor agonist — this dual action makes it different from single-mechanism weight loss medications. It activates two natural hormone pathways that regulate appetite and food intake.
- GIP and GLP-1 activation signals to your brain that you're fuller after eating less food
- It may reduce cravings and support healthier food choices
- It slows how quickly food leaves your stomach, helping you feel satisfied longer
- It supports healthy blood sugar and fat utilisation
Clinical trials showed that Mounjro helped participants lose an average of 15–21% of their body weight — though individual results vary significantly and weight loss is achieved alongside a reduced-calorie diet and increased physical activity, not as a standalone treatment.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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 Access
In the UK, Mounjro may be prescribed to adults with a BMI of 30 or above, or BMI of 27–29.9 with at least one weight-related health condition such as type 2 diabetes, high blood pressure, or sleep apnoea. You can use our free BMI calculator to check your personal BMI and understand where you fall on the NHS healthy weight scale.
Access is available through NHS specialist weight management services or private prescribing following an online clinical assessment. Your GP or prescriber will assess your individual health and suitability before prescribing. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds may apply due to higher cardiovascular risk at lower weights.
- 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 Mounjro the same as Ozempic?
No. Both contain semaglutide (different medication — Mounjro contains tirzepatide), but Ozempic is approved for type 2 diabetes, not weight loss in the UK. Wegovy is the licensed semaglutide option for weight management. Mounjro's dual mechanism (GIP+GLP-1) differs from single GLP-1 medications.
What dose do you start on with Mounjro?
You start on 2.5 mg once weekly, then increase gradually — typically by 2.5 mg every 4 weeks — up to a maximum of 15 mg. Your prescriber will determine your dose based on your response and tolerance.
What are the main side effects of Mounjro?
Very common side effects include nausea, diarrhoea, constipation, and stomach pain — usually mild and temporary. Less common are injection site reactions, fatigue, and hair loss. Serious side effects like severe stomach pain requiring urgent medical attention are rare but require immediate GP contact.
Can I get Mounjro through the NHS?
Mounjro is available through NHS specialist tier 3 weight management services in some areas, but access varies significantly by region and availability can be limited. Many people access it privately through GPhC-registered pharmacies following an online clinical assessment with a UK-licensed prescriber.
How quickly does Mounjro lead to weight loss?
Weight loss typically becomes noticeable after 4–8 weeks, with most significant loss occurring between weeks 12–24. This varies based on dose, individual metabolism, diet, and exercise. Try our GLP-1 weight loss calculator to see potential projections at different doses.
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.