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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Does Mounjaro Work For Everyone?
Mounjaro (tirzepatide) doesn't work the same way for everyone — results vary significantly between individuals based on genetics, lifestyle, and health factors. Clinical trials showed an average weight loss of 15–21% of body weight, but individual outcomes range from modest loss to substantial results. Access in the UK depends on whether you pursue NHS specialist services or private prescription routes, both with different timelines and costs. Understanding how Mounjaro effectiveness varies, combined with what you'll realistically pay and how to access it, helps you make an informed decision about whether this prescription injection is right for you.
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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.
How Effective Is Mounjaro — And Why Results Vary
Clinical trials for Mounjaro showed participants lost an average of 15–21% of their body weight at the highest dose (15 mg), though individual results ranged from 5% to over 20%. Why does effectiveness vary so much? Several key factors influence how well Mounjaro works: genetics play a role in how your body responds to tirzepatide; adherence to the injection schedule matters — missing doses reduces effectiveness; diet and physical activity are essential — Mounjaro works best alongside a reduced-calorie diet and increased activity; underlying health conditions like type 2 diabetes or thyroid disorders can affect response; and some people's bodies simply respond more strongly to GLP-1 and GIP receptor stimulation than others.
Age, starting weight, and previous weight loss attempts also influence outcomes. Younger people and those with less severe obesity sometimes lose weight more quickly initially. Importantly, Mounjaro is not a assures — some people lose significant weight, others see modest results, and a small percentage experience minimal change. This is why dose titration (gradually increasing from 2.5 mg to 15 mg) happens over 20+ weeks — your prescriber monitors your response and adjusts accordingly.
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 Access Routes: NHS Specialist Services vs Private Prescription
NHS Access: Mounjaro is NICE-approved for NHS use through specialist tier 3 and 4 weight management services. You'll need a referral from your GP to a specialist service in your area (ICB). The advantage is cost — medication is free on the NHS. The disadvantage: waiting lists are substantial in most regions, often 6–18 months or longer depending on your local service capacity. Not all regions have equal access. Your GP can discuss NHS options and check current waiting times for your area.
Private Access: Available through GPhC-registered online prescribers following an online clinical assessment — no NHS referral needed. Private tirzepatide costs vary by dose, typically £129–£220 per month. Treatment is faster to access (days or weeks rather than months), but you pay the full cost. Use our GLP-1 weight loss calculator to estimate potential results at different doses, and our BMI calculator to check your current eligibility threshold.
- 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.
Will Mounjaro definitely help me lose weight?
No, results aren't assured and vary significantly. Clinical trials showed average weight loss of 15–21%, but individual results ranged from 5% to over 20%. Success depends on genetics, adherence to injections, diet quality, physical activity, and how your body responds to tirzepatide. A prescriber will assess whether it's suitable for you.
How much does Mounjaro cost on the NHS in the UK?
Mounjaro is free on the NHS for eligible patients, but access is through specialist weight management services requiring a GP referral. Waiting times vary by region (typically 6–18 months or longer). Not all areas have equal access — ask your GP about your local tier 3 service availability and current waiting lists.
What's the cost of private Mounjaro prescription in the UK?
Private tirzepatide costs typically range from £129–£220 per month depending on the dose you're on and which provider prescribes it. Private access is faster (days to weeks) than NHS routes but you pay the full cost. Always verify the exact price with your chosen prescriber before starting.
Can I get Mounjaro on prescription through my GP?
Not directly — GPs do not typically prescribe Mounjaro for weight management. You need referral to an NHS specialist weight management service (tier 3/4), or you can access it privately through a GPhC-registered online prescriber following a clinical assessment. Check your local ICB availability first.
Does Mounjaro work better than Wegovy for weight loss?
Clinical trials suggest Mounjaro may produce slightly higher average weight loss (15–21% vs ~15% for Wegovy), but both are effective. Mounjaro uses a dual GIP+GLP-1 mechanism versus Wegovy's single GLP-1 mechanism. Individual response varies significantly — what works best depends on your personal health profile, which a prescriber will assess.
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.