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
Mounjaro Before and After — UK Evidence and Real Expectations
Mounjaro (tirzepatide) is a prescription-only weight loss injection now available in the UK through NHS specialist services and private prescribing. If you're wondering what realistic results look like, this guide covers clinical trial data, NHS eligibility criteria, and what to expect when starting treatment. Individual results vary significantly based on dose, lifestyle changes, and personal factors — there's no assured outcome.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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 Clinical Trial Data for Mounjaro in the UK
The SURMOUNT-1 clinical trial provides the clearest UK-relevant evidence for Mounjaro effectiveness. Participants receiving tirzepatide alongside a reduced-calorie diet and increased physical activity achieved an average weight loss of approximately 15–21% of their body weight over 72 weeks, depending on dose. At the maximum 15 mg dose, participants lost roughly 20.9% on average — though individual results ranged from minimal to over 30% loss.
In the UK, NICE has approved tirzepatide for use within NHS tier 3 specialist weight management services. To access Mounjaro through the NHS, you typically need a BMI of 30 or above, or 27–29.9 with a weight-related health condition such as type 2 diabetes, high blood pressure, or sleep apnoea. South Asian, Chinese, Black African, and Black Caribbean adults may qualify at lower BMI thresholds. NHS access involves referral to a specialist weight management service — availability and waiting times vary significantly by region and ICB funding.
Try our free GLP-1 weight loss calculator above to estimate potential weight loss at different Mounjaro doses based on your starting weight.
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.
What "Before and After" Really Means — NHS vs Private Access
"Before and after" weight loss results you see online often don't tell the full story. Clinical trial averages mask huge individual variation — some people lose 5% of body weight, others lose 35% or more. Success depends on dose, adherence, diet quality, physical activity level, genetics, and underlying health conditions. NHS prescribers will set realistic expectations during your clinical assessment and monitor progress at regular intervals using our free progress tracker to log changes over time.
In the UK, you can access Mounjaro through NHS tier 3 specialist services (longer waits, free treatment) or private online prescribing (faster access, private cost). Both routes require a clinical assessment to confirm you're eligible. A prescriber will discuss realistic timelines — significant results typically emerge after 8–12 weeks, with continued loss over 6–12 months. Using our BMI calculator beforehand helps establish your starting point and track progress accurately.
- 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 average weight loss with Mounjaro in the UK?
The SURMOUNT-1 clinical trial showed average weight loss of 15–21% of body weight over 72 weeks at therapeutic doses, alongside diet and exercise. This translates to roughly 10–20 kg for many people, but individual results vary significantly. Your GP or prescriber can discuss realistic expectations based on your circumstances.
Can I get Mounjaro free on the NHS in the UK?
Yes, Mounjaro (tirzepatide) is approved by NICE for NHS use within tier 3 specialist weight management services. Access is free but requires specialist referral from your GP and depends on local ICB funding. Waiting times vary significantly by region — some areas have lengthy queues. Private online prescribing offers faster access at a cost.
How long does it take to see results with Mounjaro?
Most people notice initial effects (reduced appetite, fullness) within the first 2–4 weeks. Meaningful weight loss typically becomes visible after 8–12 weeks. Significant results accumulate over 6–12 months as doses are gradually increased. Individual timelines vary based on dose and lifestyle factors.
Is Mounjaro the same as Wegovy or Ozempic in the UK?
No. Mounjaro (tirzepatide) is a dual GIP and GLP-1 medication. Wegovy is a GLP-1-only medication (semaglutide). Ozempic is also semaglutide but licensed for diabetes, not weight loss. Mounjaro often produces slightly more weight loss in trials, but individual response varies. Your prescriber will advise which suits you best.
What happens if I stop taking Mounjaro — will I regain the weight?
Weight regain is common after stopping any weight loss medication. Clinical data shows people typically regain approximately 50% of lost weight within a year of stopping. This is why ongoing lifestyle changes (diet, activity) are crucial. Your prescriber may discuss maintenance strategies before stopping treatment.
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.