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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Should I Go On Mounjaro? What You Need to Know
Deciding whether Mounjaro (tirzepatide) is right for you depends on your eligibility, health goals, and preference for NHS or private access. This prescription-only weight management injection is approved in the UK and may help support weight loss alongside lifestyle changes, but it's not suitable for everyone. Here's what you need to know about accessing Mounjaro through the NHS or privately, what the evidence shows, and how to assess whether it might be appropriate for your situation.
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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.
NHS Eligibility and How to Access Mounjaro in the UK
NHS access to Mounjaro is available through specialist tier 3 weight management services, but only if you meet specific criteria. You're eligible if you have a BMI of 30 kg/m² or above, or a BMI of 27–29.9 kg/m² with at least one weight-related health condition such as type 2 diabetes, high blood pressure, abnormal blood fats, obstructive sleep apnoea, or cardiovascular disease. If you're of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds may apply. NICE has approved tirzepatide for use in NHS specialist services, but availability varies significantly by region. You'll need a referral from your GP to tier 3 services, and waiting times can be substantial in many areas. Once assessed, your prescriber will consider your medical history, current medications (particularly oral contraceptives and diabetes treatments), and whether Mounjaro is clinically appropriate. The KwikPen auto-injector is administered once weekly, starting at 2.5 mg and increasing gradually over weeks to a maximum of 15 mg, depending on response and tolerability.
Clinically BackedWeight Loss
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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.
NHS vs Private Mounjaro Access — What Are Your Options?
Private access is an alternative if NHS waiting lists are long or tier 3 services aren't available in your area. Through private online prescribing services registered with the GPhC, you can access Mounjaro following a clinical assessment with a UK-licensed prescriber. This route typically costs between £150 and £250 per month depending on your dose. Private prescribers assess your eligibility and suitability just as rigorously as the NHS, reviewing your BMI, health conditions, medications, and contraindications. Some people choose private access for faster initiation; others prefer NHS prescribing for cost reasons. Whichever route you consider, Mounjaro works best combined with a reduced-calorie diet and increased physical activity. Clinical trials showed participants lost an average of 15–21% of their body weight, but individual results vary significantly. Consider your budget, patience for NHS waiting times, and preference for ongoing support when deciding.
- 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 is Mounjaro and how does it work?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — a prescription injection that activates two natural hormone pathways to help regulate appetite and support feeling fuller after meals. It's administered once weekly using a KwikPen auto-injector and is licensed in the UK for weight management in eligible adults.
Am I eligible for Mounjaro on the NHS?
You're eligible if you have a BMI of 30 kg/m² or above, or 27–29.9 kg/m² with weight-related health conditions like type 2 diabetes, high blood pressure, or cardiovascular disease. South Asian and Black heritage adults may have lower thresholds. Your GP can refer you to specialist tier 3 services for assessment.
What are the main side effects of Mounjaro?
Very common side effects include nausea, diarrhoea, vomiting, constipation, and stomach pain. These often improve over time as your body adjusts. Less common side effects include fatigue, dizziness, injection site reactions, and hair loss. Seek immediate medical attention for severe stomach pain or allergic reactions.
How much weight can I expect to lose on Mounjaro?
Clinical trials showed an average weight loss of 15–21% of body weight over 72 weeks, alongside a reduced-calorie diet and increased physical activity. However, individual results vary significantly — some people lose more, others less. Your prescriber can discuss realistic expectations based on your situation.
How quickly can I access Mounjaro — NHS or private?
NHS access involves a GP referral to tier 3 services, with waiting times ranging from weeks to many months depending on your region. Private access via online prescribing is typically faster — often 1–2 weeks from consultation to first injection — but costs £150–£250 monthly. Both routes require clinical assessment.
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.