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 Mounjaro Medication?
Mounjaro (tirzepatide) is a prescription-only weight management injection licensed in the UK for adults with excess weight. It's a dual GIP and GLP-1 receptor agonist — meaning it works on two natural hormone pathways to help regulate appetite and support feeling fuller after meals. Mounjaro is administered as a once-weekly injection using a pre-filled KwikPen device. Understanding how it works, who's eligible, and what to expect is essential before considering this medication. Our free BMI calculator can help you check where you currently stand, and our GLP-1 weight loss calculator can estimate potential outcomes at different doses.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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 and What Makes It Different
Mounjaro works by activating two hormone pathways: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1). This dual mechanism differentiates it from other weight loss medications like Wegovy, which activates GLP-1 only. The medication helps regulate appetite, reduces food cravings, and supports feeling satisfied after smaller meals. It also slows how quickly food leaves your stomach, though this effect typically reduces over time. Mounjaro is not insulin and doesn't work the same way as diabetes insulin treatments. Clinical trials showed that participants using Mounjaro lost an average of 15–21% of their body weight over 72 weeks, alongside a reduced-calorie diet and increased physical activity. However, individual results vary significantly — weight loss depends on many factors including starting weight, lifestyle changes, dose, and personal metabolism.
- Dual GIP + GLP-1 mechanism (more comprehensive than single-pathway medications)
- Once-weekly injection (easier than daily medications)
- Doses range from 2.5 mg to 15 mg
- Results achieved alongside dietary and lifestyle changes
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, Doses, and How to Access Mounjaro
In the UK, Mounjaro may be prescribed for adults with a BMI of 30 or above, or BMI of 27–29.9 with weight-related health conditions such as type 2 diabetes, prediabetes, high blood pressure, or cardiovascular disease. South Asian, Chinese, Black African, and Black Caribbean adults may be eligible at lower BMI thresholds due to higher health risks at these weights. Mounjaro is available through NHS specialist tier 3 weight management services (with regional variation and potential waiting lists) or privately through GPhC-registered online pharmacies following a clinical assessment. The standard dose progression starts at 2.5 mg weekly, with increases every 4 weeks up to a maximum of 15 mg. Your prescriber will assess your individual suitability, medical history, and any current medications before prescribing.
- NHS access via specialist weight management referral from your GP
- Private access via online clinical assessment with a UK-licensed prescriber
- Must be assessed individually — not suitable for everyone
- 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. Both are prescription weight loss injections, but Mounjaro (tirzepatide) is a dual GIP + GLP-1 agonist, while Wegovy (semaglutide) is a GLP-1-only agonist. In clinical trials, Mounjaro achieved slightly higher average weight loss (15–21% vs ~15% for Wegovy), but individual results vary. Your GP or prescriber can discuss which might be more suitable for you.
How do I get Mounjaro on the NHS in the UK?
Ask your GP for a referral to your local tier 3 specialist weight management service. They assess your eligibility and manage your prescription. Availability and waiting times vary significantly by region. Private access is available through online prescribing without an NHS referral, though this involves a cost.
What are the most common side effects of Mounjaro?
The most common side effects are nausea, diarrhoea, constipation, vomiting, and stomach pain. These are usually mild and often improve over time as your body adjusts. Serious side effects are rare but include severe stomach pain (possible pancreatitis) or serious allergic reactions — seek immediate medical attention if these occur.
Can I use Mounjaro if I'm on other medications?
Mounjaro may affect how your body absorbs some oral medications, particularly oral contraceptives — women taking these should use additional contraception for 4 weeks after starting and after each dose increase. Always tell your prescriber about all medications you take so they can assess interactions.
How quickly will I lose weight on Mounjaro?
Weight loss varies between individuals. Clinical trials showed average weight loss of 15–21% over 72 weeks alongside diet and exercise changes. Most people experience gradual loss rather than rapid change. Your GLP-1 weight loss calculator can provide a rough estimate based on dose, but your prescriber and lifestyle choices will significantly influence actual results.
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.