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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Mounjaro Weight Loss Medication — How It Works in the UK
Mounjaro (tirzepatide) is a prescription-only weekly weight loss injection licensed in the UK for adults with obesity or excess weight and weight-related health conditions. It works by activating two natural hormone pathways (GIP and GLP-1) to help reduce appetite and support feeling fuller after meals. In clinical trials, people lost an average of 15–21% of their body weight when using Mounjaro alongside a reduced-calorie diet and increased physical activity. This guide explains NHS eligibility, how to access it, and what the evidence shows about this weekly weight loss injection.
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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 Access Routes for Mounjaro
In the UK, Mounjaro is available through two routes: NHS specialist weight management services (tier 3) and private prescription. NHS eligibility 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 sleep apnoea. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower thresholds apply (from 27.5 kg/m²) because these groups face higher health risks at lower weights.
Accessing Mounjaro on the NHS: You must be referred by your GP to a specialist tier 3 weight management service in your region. These services provide comprehensive assessment, prescription, and ongoing monitoring. However, NHS availability varies significantly across the UK, and waiting lists can be very long. NICE has approved tirzepatide for use within NHS specialist services, but access depends on your local integrated care board (ICB) resources. Use our free BMI calculator above to check if you fall within the eligibility range for your height and ethnicity.
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.
Private Access and Cost Comparison
Private access to Mounjaro is available through GPhC-registered online pharmacies following a clinical assessment with a UK-licensed prescriber. This route does not require NHS referral and allows faster access, typically within days rather than months. Costs vary by dose and provider, ranging from approximately £150–£320 per month depending on whether you're in the starting phase (2.5 mg) or on a maintenance dose (up to 15 mg). Dose titration occurs gradually over 16+ weeks, with weekly injections delivered as a pre-filled KwikPen. Private prescribers assess your medical history and eligibility independently. Both NHS and private routes require clinical assessment and are prescription-only — Mounjaro cannot be purchased without a prescription.
- 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 the difference between Mounjaro and Wegovy?
Both are weekly weight loss injections licensed in the UK, but work differently. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, while Wegovy (semaglutide) is GLP-1 only. Clinical trials showed Mounjaro achieved slightly higher average weight loss (20.9% vs 14.9%), but individual results vary significantly. Your GP or prescriber will advise which is more suitable for you.
How long does it take to see weight loss results with Mounjaro?
Weight loss typically begins within 2–4 weeks, with steady progress over 12–16 weeks as your dose increases. The titration schedule starts at 2.5 mg and increases weekly until reaching your maintenance dose. Most weight loss occurs between weeks 4 and 20. Results depend on diet, exercise, and individual metabolism — use our weight loss calculator to project potential outcomes.
Can I get Mounjaro on the NHS in my area?
Availability depends on your local integrated care board. Ask your GP to refer you to your regional tier 3 weight management service. They will assess your eligibility based on BMI and health conditions. NHS waiting lists vary from weeks to over a year. If NHS access is limited in your area, private prescription is an alternative route.
What are the main side effects of Mounjaro?
Very common side effects include nausea, diarrhoea, constipation, and stomach pain, especially during the first few weeks. These often improve over time. Less common but serious side effects include severe stomach pain (possible pancreatitis) and gallbladder problems. Always report persistent or severe symptoms to your prescriber immediately.
Is Mounjaro suitable for type 2 diabetes management?
Mounjaro is licensed in the UK specifically for weight management in adults, not for diabetes treatment. However, weight loss itself improves blood sugar control. If you have type 2 diabetes and are overweight, discuss with your GP whether Mounjaro or other weight management approaches suit your overall diabetes care plan.
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.