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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When Was Mounjaro Invented and How It Came to the UK
Mounjaro (tirzepatide) was developed by Eli Lilly and Company and was first approved by regulatory authorities in 2022. The medication arrived in the UK market in 2023, following MHRA approval and subsequent NICE guidance for weight management. Understanding Mounjaro's development history and NHS context helps explain why it's become an important option for adults struggling with weight management across the UK. This guide covers the invention timeline, regulatory approval, and how you can access it today.
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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.
Mounjaro's Development and UK Approval Timeline
Tirzepatide development: Eli Lilly Company researched and developed tirzepatide as a dual GIP and GLP-1 receptor agonist, representing a significant advancement beyond earlier single-action GLP-1 medications. Clinical trials, particularly the SURMOUNT trials, demonstrated that this dual-action mechanism helped participants lose an average of 15–21% of their body weight when combined with dietary changes and increased physical activity.
UK regulatory approval: Mounjaro received MHRA (Medicines and Healthcare products Regulatory Authority) approval in 2023 and was designated with a Black Triangle (▼) status due to its relatively new status in the market. NICE (National Institute for Health and Care Excellence) subsequently issued guidance recommending tirzepatide for use within NHS tier 3 specialist weight management services. The Mounjaro KwikPen device became available through both NHS specialist services and private prescription routes in the UK.
NHS eligibility: Adults with 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, may be eligible. South Asian, Chinese, Black African, and Black Caribbean adults may qualify at lower BMI thresholds due to higher cardiovascular risk at these levels.
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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.
How to Access Mounjaro in the UK: NHS vs Private Routes
NHS access through tier 3 services: Mounjaro is prescribed through specialist multidisciplinary weight management services, typically accessed by GP referral. However, NHS availability varies significantly by region, and waiting times can be lengthy in many areas. Regional integrated care boards (ICBs) determine local provision and eligibility criteria.
Private prescribing: UK-licensed prescribers offer online consultations for Mounjaro, with prescriptions dispensed by GPhC-registered pharmacies. This route does not require NHS referral and can often be accessed more quickly, though at private cost. A clinical assessment is always required before prescription, regardless of route. Use our GLP-1 weight loss calculator to estimate potential outcomes, and our BMI calculator to confirm your eligibility status before consulting a prescriber.
- 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.
When exactly was Mounjaro first approved in the UK?
Mounjaro (tirzepatide) received MHRA approval in 2023 and became available through NHS specialist services and private prescribing shortly after. NICE issued guidance supporting its use in tier 3 weight management services.
How does Mounjaro differ from older weight loss medications like Saxenda?
Mounjaro is a dual GIP and GLP-1 receptor agonist, while Saxenda (liraglutide) is a single GLP-1 agonist. The dual mechanism in tirzepatide may support greater average weight loss, though individual results vary significantly.
Is Mounjaro available on the NHS in the UK?
Yes, Mounjaro is available through NHS tier 3 specialist weight management services following GP referral. However, availability and waiting times vary by region. Private prescribing offers an alternative route through online clinical assessment.
What does the Black Triangle (▼) status on Mounjaro mean?
Black Triangle designation indicates the medication is under additional MHRA monitoring due to its recent approval. This is a safety precaution and does not mean the medication is unsafe—it means healthcare professionals should report any suspected side effects promptly.
How does Mounjaro compare to Wegovy for weight management in the UK?
Both are prescription-only weight management medications available in the UK. Mounjaro (tirzepatide) uses dual GIP/GLP-1 action while Wegovy (semaglutide) is GLP-1 only. Clinical trial data suggests Mounjaro may support slightly greater average weight loss, though results vary between individuals. Your prescriber will advise which is more suitable.
Ready to take control of your weight loss journey?
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