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
Who Makes Mounjaro and How Does It Work?
Mounjaro is manufactured by Eli Lilly and Company, a major pharmaceutical manufacturer. The active ingredient is tirzepatide, a dual GIP and GLP-1 receptor agonist that works differently from other weight management injections available in the UK. It's a prescription-only medicine approved for adults with obesity or overweight with weight-related health conditions. Understanding who makes Mounjaro and how it functions can help you have informed conversations with your GP about whether this treatment might be suitable for you.
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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 — The Tirzepatide Mechanism
Mounjaro's manufacturer, Eli Lilly, developed tirzepatide as a dual-action weight management injection. Unlike single-mechanism GLP-1 medicines like Wegovy (semaglutide), Mounjaro activates both GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 receptor pathways. This dual action may help regulate appetite more effectively, reduce food cravings, and support feeling fuller after smaller meals. The medication also slows gastric emptying, meaning food leaves your stomach more gradually. In clinical trials (SURMOUNT-1), participants using Mounjaro lost an average of 15–21% of their body weight over 72 weeks — though individual results vary significantly. Mounjaro is supplied as a pre-filled KwikPen device for once-weekly injection. It's a prescription-only medicine, meaning you'll need a clinical assessment from a UK-licensed prescriber before it can be 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.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
UK Access and Eligibility for Mounjaro
In the UK, Mounjaro is available through NHS specialist tier 3 weight management services and private online prescribing. NHS eligibility typically requires a BMI of 30 or above, or 27–29.9 with weight-related health conditions like type 2 diabetes, high blood pressure, or sleep apnoea. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds (27.5+) may apply due to higher health risks at lower weights. You'll need a referral from your GP to NHS services, though waiting lists vary by region. Private access is available without NHS referral through GPhC-registered pharmacies following an online clinical assessment. Use our free BMI calculator above to check whether you might fall within typical eligibility ranges, then discuss options with your GP.
- 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 made by the same company as Ozempic?
No. Mounjaro (tirzepatide) is made by Eli Lilly and Company. Ozempic (semaglutide) is made by Novo Nordisk. Both are injectable weight management medications, but they have different manufacturers, mechanisms, and doses. Mounjaro is a dual GIP/GLP-1 agonist, while Wegovy (also semaglutide, also Novo Nordisk) is a single GLP-1 agonist.
What does tirzepatide do in Mounjaro?
Tirzepatide is the active ingredient in Mounjaro. It mimics two natural hormones — GIP and GLP-1 — to help reduce appetite, support feeling fuller, slow digestion, and regulate blood sugar. This dual mechanism may provide more effective weight management than single-action medications. Clinical trials showed an average weight loss of 15–21% of body weight, though results vary between individuals.
Can I get Mounjaro on the NHS in the UK?
Mounjaro is available through NHS specialist tier 3 weight management services if you meet eligibility criteria (BMI ≥30, or ≥27 with weight-related health conditions). Access requires a GP referral and varies significantly by region. Waiting lists can be lengthy in some areas. Private access is also available through online prescribing without NHS referral.
How often do I inject Mounjaro?
Mounjaro is a once-weekly injection. Each pre-filled KwikPen contains four weekly doses. Doses start at 2.5 mg and increase gradually every 4 weeks, with a maximum dose of 15 mg weekly. Your prescriber will advise on dose escalation based on your individual response and tolerance. Our GLP-1 weight loss calculator can help you estimate potential outcomes at different doses.
What are the main side effects of Mounjaro in the UK?
Very common side effects include nausea, diarrhoea, vomiting, constipation, and stomach pain — these often improve with time. Common side effects include indigestion, fatigue, dizziness, and injection site reactions. Serious but rare side effects include pancreatitis (severe stomach pain) and gallbladder problems. Always report new or concerning symptoms to your GP. Full information is available in the patient information leaflet provided with your prescription.
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.