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 Is Mounjaro? A Complete UK Health Guide
Mounjaro is a prescription-only weight management injection licensed in the UK for adults with excess weight and related health conditions. It contains tirzepatide, a dual GIP and GLP-1 receptor agonist that works differently from other weight loss medications available in the UK. This guide explains how Mounjaro works, who can access it through the NHS or privately, expected outcomes based on clinical trial data, and important safety information to discuss with your GP or prescriber.
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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 and What to Expect
Mounjaro activates two natural hormone pathways — GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) — which is what makes it unique compared to single-mechanism weight loss medications. This dual action may help regulate appetite, reduce food cravings, and support feeling fuller after smaller meals. It also slows gastric emptying, meaning food moves through your stomach more slowly, which can help extend feelings of fullness.
Clinical trials (the SURMOUNT studies) showed that adults taking Mounjaro alongside a reduced-calorie diet and increased physical activity lost an average of 15–21% of their body weight, depending on dose. However, individual results vary significantly. The medication is not insulin and does not work the same way as insulin therapy. Use our free GLP-1 weight loss calculator to estimate potential weight loss projections at different Mounjaro doses, and our BMI calculator to understand your personal weight health baseline.
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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 Eligibility, Doses, and Access Routes
You may be eligible for Mounjaro in the UK if you have a BMI of 30 or above, or a BMI of 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. South Asian, Chinese, Black African, or Black Caribbean adults may qualify at lower BMI thresholds (from BMI 27.5 or above) because these groups face higher health risks at lower weights. Mounjaro is available through NHS specialist weight management services (tier 3/4) following GP referral, though NHS availability and waiting times vary significantly by region. It is also available through private prescribing following an online clinical assessment with a UK-licensed prescriber. Doses range from 2.5 mg to 15 mg, increasing weekly over several weeks under prescriber guidance.
- 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 Ozempic?
No. Both contain semaglutide, but Ozempic is licensed for type 2 diabetes (doses up to 2 mg) and is not approved for weight loss in the UK. Mounjaro contains tirzepatide, a different medication with a dual mechanism. Wegovy is the semaglutide weight loss version in the UK.
What are the most common side effects of Mounjaro?
Common side effects include nausea, diarrhoea, vomiting, constipation, and stomach pain — especially when starting or increasing doses. These often improve over time. Serious side effects are rare but include severe stomach pain (possible pancreatitis) and allergic reactions. Always discuss side effects with your prescriber.
How much weight can I expect to lose on Mounjaro?
Clinical trials showed average weight loss of 15–21% of body weight over 72 weeks, but results vary. Some people lose more, some less. Weight loss depends on dose, adherence, diet, physical activity, and individual metabolism. Your prescriber can discuss realistic expectations based on your personal health.
Can I get Mounjaro on the NHS in the UK?
Yes, Mounjaro is approved by NICE for NHS specialist weight management services. Access requires referral from your GP to a tier 3/4 service. Availability and waiting times vary by region. Private access through online prescribing is also available without NHS referral.
What happens if I miss a Mounjaro injection?
If you miss a dose within 4 days, take it as soon as you remember and continue your normal schedule. If more than 4 days have passed, skip that dose and take your next injection on the scheduled day. Never double-dose. Always contact your prescriber with concerns.
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.