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 Instructions and How to Access in the UK
If you're looking for Mounjaro instructions or wondering how to access this weight loss injection in the UK, this guide covers everything you need to know. Mounjaro (tirzepatide) is a prescription-only GLP-1 and GIP receptor agonist available through both NHS specialist services and private online prescribing. This page explains the injection technique, storage, dosing schedule, and the two main routes to getting a prescription in the UK — including typical costs and what to expect during the clinical assessment process.
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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.
How Mounjaro Works and Basic Injection Instructions
Mounjaro is a once-weekly injectable medication supplied as a pre-filled KwikPen device. Each pen contains four weekly doses and comes pre-loaded with the solution — you do not need to mix or prepare anything.
Injection technique: Mounjaro is injected under the skin (subcutaneously) once per week, on the same day each week. The three main injection sites are the stomach (abdomen), upper thigh, or upper arm — rotate sites each week to prevent irritation. Pinch the skin, insert the needle at a 90-degree angle, hold for 3 seconds, then release. The pen makes a clicking sound when the dose is complete.
Storage is critical: Unopened pens must be refrigerated at 2–8°C (do not freeze). After first use, the pen can be stored at room temperature (below 30°C) for up to 30 days, then must be disposed of. Keep in the original carton to protect from light.
Detailed illustrated instructions are provided with each pen, and your prescriber will also demonstrate the injection technique during your consultation.
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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.
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Mounjaro Cost in the UK: NHS vs Private Access
NHS access: Mounjaro is available through NHS specialist tier 3 weight management services, but availability is very limited and regional. You must be referred by your GP to a specialist service, and waiting lists can be months to years in some areas depending on your local ICB (integrated care board).
Private access: Through private online prescribing, Mounjaro costs typically range from £150–£320+ per month depending on dose and provider. At higher doses (10 mg–15 mg), costs approach the upper end. Private prescriptions are issued following an online clinical assessment by a UK-licensed prescriber, and dispensed by a GPhC-registered pharmacy. This route does not require an NHS referral.
Use our GLP-1 weight loss calculator to explore projected outcomes at different doses, and check your BMI with our free tool to understand your eligibility baseline.
- 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 inject Mounjaro — which site is best?
Rotate between your stomach (most common), upper thigh, or upper arm each week. Pinch skin, insert at 90 degrees, inject, hold 3 seconds. Your prescriber will show you how during your consultation. Changing injection sites reduces irritation and bruising. Do not inject into areas with scars or bruised skin.
Can I get Mounjaro free on the NHS?
Mounjaro is available on the NHS through specialist weight management services, but access is very limited and varies by region. You need a GP referral to a tier 3 service — waiting lists are often several months to years. Ask your GP whether your local ICB funds tirzepatide and what the referral process is.
How much does Mounjaro cost privately in the UK?
Private Mounjaro costs typically range from £150–£320+ per month depending on the dose. Starting doses (2.5 mg–5 mg) are cheaper; higher maintenance doses (10 mg–15 mg) cost more. Prices vary between providers, so it's worth comparing online prescribing services. Most GPhC-registered services offer the same medication at different price points.
What if I miss a Mounjaro injection?
If you remember within 4 days of the missed dose, inject as soon as you can and continue your normal schedule the following week. If more than 4 days have passed, skip the missed dose and take your next dose on your normal day. Never take two doses within 3 days of each other.
What's the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist; Wegovy (semaglutide) is GLP-1 only. Mounjaro starts at 2.5 mg and goes up to 15 mg weekly. Wegovy starts at 0.25 mg and maxes at 2.4 mg weekly. Clinical trials showed Mounjaro produced slightly higher average weight loss (~21% vs ~15%), but individual results vary. Both are prescription-only and available privately or through NHS specialist services.
Ready to take control of your weight loss journey?
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