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
Should I Try Mounjaro? NHS Eligibility and UK Guidance
Whether Mounjaro is right for you depends on your weight, health conditions, and NHS or private access options. Mounjaro (tirzepatide) is a prescription-only, once-weekly injection licensed in the UK for weight management. This guide explains NHS eligibility criteria, how the medication works, and the routes to access it — helping you decide if it's appropriate for your individual circumstances. Always consult your GP before starting any weight loss treatment.
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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.
Who Is Eligible for Mounjaro on the NHS and Privately
NHS eligibility for Mounjaro is available through tier 3 specialist weight management services, typically requiring GP referral. You may be eligible 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, prediabetes, high blood pressure, or sleep apnoea. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower thresholds may apply (BMI 27.5+). Use our free BMI calculator above to check your personal BMI instantly. NICE has approved tirzepatide for NHS use, but regional availability varies significantly — some areas have long waiting lists. Privately, you can access Mounjaro through a UK-licensed prescriber's online assessment without NHS referral. Eligibility criteria are similar, and prescriptions are dispensed by GPhC-registered pharmacies. A clinical assessment is always required before prescription, regardless of route.
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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.
How Mounjaro Works and Expected Results
Mounjaro (tirzepatide) works as a dual GIP and GLP-1 receptor agonist — activating two natural hormone pathways to help regulate appetite and support feeling fuller after smaller meals. Clinical trials (SURMOUNT-1) showed that participants on the maximum 15mg dose lost an average of approximately 20.9% of their body weight over 72 weeks, alongside a reduced-calorie diet and increased physical activity — though individual results vary significantly. It takes 16–20 weeks to reach the maximum dose, as the medication is titrated gradually from 2.5mg. Common side effects include nausea, diarrhoea, and constipation, often improving over time. Try our GLP-1 weight loss calculator to see projected results at different doses based on your current weight.
- 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's the difference between Mounjaro and Wegovy?
Both are prescription-only weight loss injections, but Mounjaro (tirzepatide) is a dual GIP+GLP-1 agonist, while Wegovy (semaglutide) is a GLP-1 agonist only. Mounjaro's dual mechanism may offer greater average weight loss in clinical trials. Starting doses, maximum doses, and injection schedules differ. Your prescriber can advise which suits you.
Can I get Mounjaro through the NHS?
Yes, NICE has approved tirzepatide for NHS use through tier 3 specialist weight management services. You'll need a GP referral, and eligibility criteria apply. However, NHS availability varies by region and waiting lists can be lengthy. Private access is faster and doesn't require NHS referral.
How long does it take to see weight loss results on Mounjaro?
Weight loss typically begins within the first few weeks, but results accelerate as your dose increases. The full benefit is usually seen after reaching your maintenance dose (weeks 16–20+). Results vary — some people lose more than others. Sustainable weight loss of 0.5–1kg per week is typical alongside diet and exercise.
What side effects should I expect from Mounjaro?
Very common side effects include nausea, diarrhoea, vomiting, constipation, and stomach pain — particularly when starting or increasing doses. Most side effects improve over time. Serious side effects are rare but include severe stomach pain (possible pancreatitis) and allergic reactions. Always report concerning symptoms to your prescriber.
Is Mounjaro suitable if I have type 2 diabetes?
Yes, having type 2 diabetes or prediabetes is a weight-related health condition that may increase your eligibility for Mounjaro. However, if you take diabetes medications like insulin or sulphonylureas, your prescriber may need to adjust doses. Always inform your prescriber of all medications and health conditions.
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.