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 UK Health Guide
Mounjaro (tirzepatide) is a prescription-only weight loss injection licensed in the UK for adults with obesity or overweight with health conditions. It's a once-weekly injectable medicine that works by activating two natural hormone pathways to help regulate appetite and support weight management. Unlike many weight loss medications, Mounjaro uses dual GLP-1 and GIP receptor agonist technology, which is why it may offer different results compared to single-mechanism alternatives like Wegovy. This guide explains how Mounjaro works, who can access it through the NHS, and what the clinical evidence shows about its effectiveness.
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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 NHS Eligibility in the UK
Mounjaro mechanism: Mounjaro activates two hormone pathways—GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1)—which work together to help regulate appetite, reduce food cravings, and support feeling fuller after smaller meals. This dual mechanism is what distinguishes tirzepatide from single GLP-1 agonists like Wegovy.
NHS eligibility criteria: The NHS prescribes Mounjaro through specialist tier 3 weight management services for adults who have:
- BMI of 30 kg/m² or above, OR
- BMI of 27–29.9 kg/m² with at least one weight-related health condition (type 2 diabetes, prediabetes, high blood pressure, abnormal blood fats, or sleep apnoea)
For South Asian, Chinese, Black African, or Black Caribbean adults, lower BMI thresholds apply (starting at BMI 27.5). Access is through your GP referral to a specialist service—availability and waiting times vary significantly by region.
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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.
NHS vs Private Access and Clinical Evidence
NHS route: Mounjaro is available through NICE-approved tier 3 specialist weight management services. You'll need a GP referral, and the specialist team will assess your eligibility and manage your treatment. Waiting lists can be lengthy in many areas.
Private route: Available through GPhC-registered online pharmacies following an online clinical assessment with a UK-licensed prescriber, without needing NHS referral.
Clinical evidence: In the SURMOUNT-1 trial, adults on Mounjaro 15 mg lost an average of 20.9% of their body weight over 72 weeks, alongside a reduced-calorie diet and increased activity. Individual results vary significantly. Use our GLP-1 weight loss calculator to estimate potential outcomes at different doses.
- 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) uses dual GIP+GLP-1 mechanism, while Wegovy (semaglutide) activates GLP-1 only. Clinical trials showed different average weight loss results, though individual outcomes vary. Your prescriber can advise which is more suitable for you.
How long does Mounjaro take to work?
Most people notice appetite changes within the first few weeks, but significant weight loss typically becomes measurable over 8–12 weeks. Each dose increase (every 4 weeks) may bring additional effects. Results depend on diet, activity, and individual response—use our progress tracker to monitor changes.
Can I get Mounjaro on the NHS in my area?
Mounjaro is approved by NICE for NHS specialist weight management services, but availability varies by region and local ICB (integrated care board). Ask your GP about referral to your local tier 3 weight management service. Waiting lists can be several months in some areas. Private access is available without NHS referral.
What happens if I stop taking Mounjaro?
Weight regain can occur once you stop the injection. That's why Mounjaro is part of a longer-term weight management plan, alongside sustained lifestyle changes—diet and physical activity. Your prescriber will discuss duration and stopping plans based on your individual situation and health goals.
How much does Mounjaro cost in the UK?
On the NHS, there's no direct cost to you (covered by the NHS). Privately, costs typically range from £150–£320 per month depending on dose and provider. Prices vary between pharmacies, so it's worth comparing. Always ensure you're using a GPhC-registered pharmacy.
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.