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 for Weight Loss — What You Need to Know
Mounjaro (tirzepatide) is a prescription-only weight loss medication licensed in the UK for adults with obesity or overweight with weight-related health conditions. It's a once-weekly injection that works differently from other weight loss drugs by activating two natural hormone pathways — GIP and GLP-1 — which may help reduce appetite and support feeling fuller after meals. This guide explains how Mounjaro works, who it's suitable for, eligibility criteria, and what to expect. Use our free GLP-1 weight loss calculator above to explore potential weight loss outcomes at different doses.
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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 as a Weight Loss Medication
Mounjaro contains tirzepatide, a dual GIP and GLP-1 receptor agonist — this dual mechanism is what makes it unique among weight loss medications. Unlike single-action GLP-1 injections such as Wegovy, Mounjaro activates both the GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) hormone pathways.
These pathways naturally signal your brain when you're full, reduce food cravings, and slow how quickly food leaves your stomach. Clinical trial data showed that participants taking Mounjaro lost an average of 15–21% of their body weight — though individual results vary significantly and depend on your starting weight, diet, and physical activity.
- Mounjaro is a weekly injection delivered via a pre-filled KwikPen device
- It's prescription-only and requires a clinical assessment before being prescribed
- Results are 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 How to Access Mounjaro
In the UK, Mounjaro may be prescribed to adults with a BMI of 30 kg/m² or above, or BMI of 27–29.9 kg/m² with weight-related health conditions including type 2 diabetes, prediabetes, high blood pressure, high cholesterol, sleep apnoea, or cardiovascular disease. South Asian, Chinese, Black African, and Black Caribbean adults may qualify at lower BMI thresholds.
Access is available through NHS specialist weight management services (tier 3 services) following a GP referral, though availability and waiting times vary significantly by region. Alternatively, Mounjaro is available privately through UK-licensed prescribers following an online clinical assessment. Calculate your BMI using our free BMI calculator to see where you fall, and discuss eligibility with your GP or a registered 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.
What doses does Mounjaro come in for weight loss?
Mounjaro starts at 2.5 mg weekly and escalates every 4 weeks through 5 mg, 7.5 mg, 10 mg, 12.5 mg, and up to a maximum of 15 mg weekly. Your prescriber will adjust your dose based on your response and tolerance to side effects. Each KwikPen contains 4 weekly doses.
How much weight can you lose with Mounjaro?
Clinical trials showed participants lost an average of 15–21% of their body weight at the highest dose over 72 weeks — alongside diet and exercise. Individual results vary widely depending on your starting weight, adherence to lifestyle changes, and how your body responds. Some people lose more, some less.
What are the common side effects of Mounjaro?
The most common side effects include nausea, diarrhoea, vomiting, and constipation — typically in the first few weeks and often improving over time. Less common side effects include injection site reactions, fatigue, headache, and hair loss. Serious side effects are rare but can include severe stomach pain and gallbladder problems.
Is Mounjaro available on the NHS in the UK?
Yes, Mounjaro is approved by NICE for NHS use in specialist weight management services (tier 3). However, access is limited and varies by region — waiting lists can be long. Your GP can refer you to your local specialist service, but you may also choose to access it privately through a UK-licensed prescriber.
How does Mounjaro differ from Wegovy for weight loss?
Mounjaro is a dual GIP and GLP-1 agonist (tirzepatide), while Wegovy is a single GLP-1 agonist (semaglutide). Clinical trials suggest Mounjaro may produce slightly greater average weight loss, but both are effective. The choice depends on individual response, side effects, and prescriber recommendation — always discuss with your healthcare provider.
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.