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
What to Expect: Mounjaro Before and After in the UK
When discussing weight loss injections like Mounjaro (tirzepatide), it's important to understand that "before and after" results vary significantly between individuals. In the UK, Mounjaro is available through NHS specialist weight management services and private prescribing routes. This guide explains NHS eligibility criteria, realistic expectations based on clinical trial data, and how the tirzepatide treatment pathway works within the UK healthcare system. Always remember that weight loss outcomes depend on many factors including diet, activity level, starting weight, and individual response to the medication.
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 Access and Eligibility for Mounjaro in the UK
In the UK, Mounjaro is licensed for weight management in adults and accessed primarily through NHS tier 3 specialist weight management services. Eligibility typically requires a BMI of 30 kg/m² or above, or 27–29.9 kg/m² with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease.
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds (from 27.5 kg/m²) apply because these populations face higher health risks at lower weights. Access via NHS specialist services means you'll be assessed by a multidisciplinary team — including doctors, dietitians, and behavioural specialists — who will evaluate whether GIP and GLP-1 receptor agonist therapy is appropriate for you. The weekly weight loss injection is prescribed as part of a comprehensive programme that includes dietary support and lifestyle changes. MHRA-monitored tirzepatide is subject to additional safety monitoring (Black Triangle ▼ status), and your prescriber will review your progress regularly using our BMI calculator and progress tracker to monitor outcomes over time.
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.
Realistic Expectations: Clinical Trial Data and Individual Variation
Clinical trials of Mounjaro (the SURMOUNT studies) showed average weight loss of approximately 15–21% of body weight over 72 weeks, depending on the dose — but individual results vary considerably. Some people lose more, some less. These results were achieved alongside a reduced-calorie diet and increased physical activity. It's crucial to understand that prescription weight loss injections are not standalone treatments; they work best as part of a comprehensive approach.
Weight loss typically becomes noticeable after 4–8 weeks of treatment, though this varies. Side effects such as nausea are common initially and often improve over time. The NHS approach emphasises sustainable, long-term weight management rather than rapid results. Use our free GLP-1 weight loss calculator to understand projected outcomes at different doses, and track your progress with our progress tracker throughout your treatment journey.
- 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.
Can I access Mounjaro through the NHS in the UK?
Yes, Mounjaro (tirzepatide) is licensed in the UK and available through NHS tier 3 specialist weight management services. You'll need to be referred by your GP and meet eligibility criteria (BMI ≥30, or ≥27 with weight-related health conditions). NHS availability varies by region, and waiting lists can be lengthy. Private access is also available through GPhC-registered online pharmacies following a clinical assessment.
How much weight can I expect to lose with Mounjaro?
Clinical trials showed average weight loss of 15–21% of body weight over 72 weeks, depending on the dose. However, individual results vary significantly based on diet, activity level, genetics, and how your body responds. Weight loss occurs alongside a reduced-calorie diet and increased physical activity. Our GLP-1 weight loss calculator can help you understand potential outcomes.
What's the difference between "before and after" photos and real-world outcomes?
Before/after imagery often shows best-case scenarios or curated examples. Real weight loss is gradual and varies between individuals. NHS specialist services focus on sustainable health improvements rather than dramatic transformations. Progress includes changes in health markers (blood pressure, blood sugar), energy levels, and how you feel — not just numbers on the scales.
How long does Mounjaro take to work?
Weight loss typically becomes noticeable after 4–8 weeks, though this varies. The dose is gradually increased over 16–20 weeks to reach the therapeutic level (up to 15 mg weekly). Many people experience reduced appetite within days, but significant weight changes take weeks to months. Your NHS team will monitor your progress at regular appointments.
What happens after I stop taking Mounjaro?
Weight can return if lifestyle changes (diet and activity) are not maintained. Mounjaro is not a permanent supports for obesity; it's a tool to support weight loss during active treatment. The NHS approach emphasises building sustainable habits alongside medication so that progress is maintained long-term. Your GP or specialist team can advise on duration of 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.