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 Are the Ingredients of Mounjaro?
Mounjaro is a prescription-only weight management injection licensed in the UK containing tirzepatide as its active ingredient. Tirzepatide is a dual GIP and GLP-1 receptor agonist — meaning it activates two natural hormone pathways to help regulate appetite and support weight loss alongside a reduced-calorie diet and increased physical activity. Understanding what Mounjaro contains and how it works can help you decide whether this medication is right for you. This guide explains the active and inactive ingredients, how to access Mounjaro in the UK, and what costs and eligibility involve.
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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.
Active Ingredient and How Mounjaro Works
Tirzepatide is the active pharmaceutical ingredient in Mounjaro. It's a synthetic peptide that mimics two natural gut hormones: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1). This dual action is what distinguishes Mounjaro from other weight management injections like Wegovy, which only activates the GLP-1 pathway. Tirzepatide works by signalling to your brain that you're full, reducing food cravings, and slowing how quickly food leaves your stomach. Clinical trials (the SURMOUNT studies) showed that on average, adults using Mounjaro lost between 15–21% of their body weight, though individual results vary significantly. The medication comes as a pre-filled KwikPen delivering once-weekly injections, with doses ranging from 2.5 mg to 15 mg. Mounjaro is prescription-only in the UK and requires a clinical assessment before being prescribed.
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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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Accessing Mounjaro in the UK: Cost and Routes
Mounjaro is available in the UK through two routes: NHS specialist weight management services or private online prescribing. NHS access is typically through tier 3 specialist services following a GP referral, though availability varies significantly by region and waiting lists can be lengthy. Private access is through GPhC-registered online pharmacies following an online consultation with a UK-licensed prescriber. Private costs typically range from £129–£320 per month depending on your dose, with no need for NHS referral. Both routes require a clinical assessment to confirm you meet eligibility criteria: BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. Use our free GLP-1 weight loss calculator above to explore potential outcomes at different doses, and our BMI calculator to check your current status.
- 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 tirzepatide and how does it differ from semaglutide?
Tirzepatide (Mounjaro) is a dual GIP and GLP-1 receptor agonist, whereas semaglutide (Wegovy) is a GLP-1-only agonist. The dual mechanism of tirzepatide activates two hormone pathways, which clinical evidence suggests may produce greater weight loss on average than GLP-1-only medications. Both are prescription-only and require clinical assessment.
What are the inactive ingredients in Mounjaro?
Each Mounjaro KwikPen contains tirzepatide plus inactive ingredients including sodium phosphate dibasic dihydrate, sodium dihydrogen phosphate dihydrate, disodium hydrogen phosphate dihydrate, sodium chloride, and water. These excipients ensure the medication remains stable and effective. If you have allergies to any ingredients, inform your prescriber.
How much does Mounjaro cost privately in the UK?
Private Mounjaro costs in the UK typically range from £129–£320 per month depending on your dose (2.5 mg to 15 mg). Each KwikPen contains 4 weekly doses. Costs vary between providers, so comparing options is worthwhile. NHS access is free but may involve longer waiting times.
Can I access Mounjaro through the NHS in the UK?
Yes, Mounjaro is NICE-approved for NHS use within specialist tier 3 weight management services. Access requires a GP referral and assessment by a multidisciplinary team. Availability and waiting times vary significantly by region. Your GP can advise whether you meet local eligibility criteria.
What's the difference between Mounjaro and Wegovy in terms of ingredients?
Mounjaro's active ingredient is tirzepatide (dual GIP/GLP-1 agonist), while Wegovy's is semaglutide (GLP-1-only agonist). This means Mounjaro activates two hormone pathways versus one. Clinical trial data suggests Mounjaro may produce slightly greater average weight loss, but individual results vary. Both are prescription-only and require clinical assessment.
Ready to take control of your weight loss journey?
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