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 Diet Injection: UK NHS Guide
Mounjaro (tirzepatide) is a prescription-only weekly weight loss injection licensed in the UK for adults with obesity or overweight with health complications. Unlike traditional diet approaches alone, this weekly weight loss injection works by activating two natural hormone pathways that may help reduce appetite and support feeling fuller after smaller meals. Access through the NHS involves referral to specialist tier 3 weight management services, though availability varies significantly across regions. Understanding your eligibility and the different access routes — NHS or private — is essential before discussing this option with your GP or a licensed prescriber.
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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.
NHS Eligibility and Specialist Services
In the UK, Mounjaro may be prescribed through NHS specialist tier 3 weight management services for adults with a BMI of 30 kg/m² or above, or a BMI of 27–29.9 with at least one weight-related health condition such as type 2 diabetes, prediabetes, high blood pressure, or cardiovascular disease. South Asian, Chinese, Black African, and Black Caribbean adults may be eligible at lower BMI thresholds due to higher health risks at lower weights.
Access to Mounjaro on the NHS requires referral from your GP to a specialist weight management service. NICE (National Institute for Health and Care Excellence) has approved tirzepatide for use within NHS weight management pathways. However, NHS availability is limited and varies significantly by region, with waiting lists often extending months or longer. Your GP can advise whether your local integrated care board (ICB) offers access and help with the referral process. Alongside this weekly weight loss injection, you'll also receive support from a multidisciplinary team including dietitians and behaviour change specialists.
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.
NHS vs Private Access Routes in the UK
NHS route: Referral-based, free at point of use, but limited availability and potentially long waits. Prescribing follows NICE guidance and is managed by specialist services alongside structured support programmes.
Private route: Available without NHS referral through GPhC-registered online pharmacies following a clinical assessment by a UK-licensed prescriber. This route offers faster access to the weekly weight loss injection but requires private payment (typically £150–£300+ per month depending on dose). Both routes require a prescription and clinical assessment — Mounjaro cannot be obtained without professional medical evaluation of your suitability, medical history, and current medications.
Understanding How Mounjaro Works and What to ExpectMounjaro is a dual GIP and GLP-1 receptor agonist, activating two natural hormone pathways that regulate appetite and blood sugar. This dual mechanism may differentiate it from single GLP-1 medications like Wegovy (semaglutide). Clinical trials showed participants lost an average of 15–21% of their body weight over 72 weeks, though individual results vary significantly. Weight loss is achieved at doses ranging from 2.5 mg (starting) to 15 mg (maximum), with dose increases every 4 weeks.
Common side effects include nausea, diarrhoea, constipation, and stomach discomfort — typically mild and reducing over time. You'll also benefit from using our free BMI calculator and weight loss projection tool to understand your starting point and potential outcomes with this weekly weight loss injection before speaking to your 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.
How do I access Mounjaro through the NHS in the UK?
Contact your GP and ask for referral to your local tier 3 specialist weight management service. Your GP will assess eligibility based on BMI and health conditions. NICE has approved tirzepatide for NHS use, but availability varies by region. Wait times can be several months or longer depending on local provision and demand.
What is the difference between Mounjaro and Wegovy?
Both are prescription weekly weight loss injections licensed in the UK. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, while Wegovy (semaglutide) is a GLP-1 agonist only. Mounjaro starts at 2.5 mg rising to 15 mg; Wegovy starts at 0.25 mg rising to 2.4 mg. Clinical trial results showed similar average weight loss, but individual response varies.
Can I get Mounjaro privately without NHS referral?
Yes. GPhC-registered online pharmacies offer private prescribing following an online clinical assessment by a UK-licensed prescriber. This route is faster than NHS but involves private payment. The prescriber will assess your suitability, medical history, and medications before issuing a prescription.
What side effects should I expect from this weekly weight loss injection?
Common side effects include nausea, diarrhoea, constipation, stomach pain, and fatigue — usually mild and improving over weeks. Serious side effects are rare but can include pancreatitis (severe stomach pain). Report any concerning symptoms to your prescriber or GP immediately.
How much weight can I expect to lose with Mounjaro?
Clinical trials showed average weight loss of 15–21% of body weight, but results vary significantly between individuals. Weight loss depends on dose, adherence, diet changes, and physical activity. Your prescriber can help estimate realistic expectations based on your individual circumstances and health history.
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.