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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How to Inject Your Mounjaro Pen Safely
If you've been prescribed Mounjaro (tirzepatide), knowing how to inject your KwikPen correctly is essential for getting the best results. This guide covers the injection technique, step-by-step instructions, UK cost context, and how to access Mounjaro through either NHS specialist services or private prescription routes. Whether you're starting at 2.5mg or escalating through the dose titration schedule up to the maximum 15mg dose, we'll walk you through everything you need to know.
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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.
Step-by-Step Mounjaro Injection Technique
Preparation: Remove your Mounjaro KwikPen from the refrigerator (2–8°C) 15–30 minutes before injection to allow it to reach room temperature. Check the liquid inside the pen window — it should be clear and colourless. Never use if it looks cloudy, discoloured, or contains particles.
- Wash your hands thoroughly with soap and water
- Wipe the injection site with an alcohol swab and allow it to dry completely
- Rotate injection sites each week (stomach, upper thigh, or upper arm with assistance)
Injection: Pinch the skin gently at your chosen site. Hold the pen at a 90-degree angle and push the needle straight into the skin. Press the activation button slowly until you hear or feel a click. Keep the pen pressed against your skin for 6 seconds after the click to ensure the full dose is delivered. Remove the pen and release the pinched skin. Each KwikPen contains 4 doses (4 weeks of injections), and you'll dispose of it 30 days after first use.
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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.
Mounjaro Cost and UK Access Routes
NHS Access: Mounjaro is available through NHS specialist tier 3 and tier 4 weight management services, subject to NICE approval. You'll need a GP referral and clinical assessment, but there is no direct cost to you. However, NHS availability varies significantly by region (Integrated Care Board), and waiting lists can be lengthy — some areas have waits exceeding 12 months. Access depends on meeting NHS eligibility criteria: BMI of 30 or above, or BMI of 27–29.9 with weight-related health conditions such as type 2 diabetes, hypertension, or obstructive sleep apnoea.
Private Access: Private prescription Mounjaro is available through UK-licensed online prescribers following a remote clinical assessment. Costs typically range from £140–£320 per month depending on dose and provider — higher doses cost more. A prescriber will assess your eligibility and medical history before issuing a prescription to a GPhC-registered pharmacy. This route is faster than NHS (typically 1–2 weeks) and doesn't require an NHS referral, but you bear the full cost.
Use our free GLP-1 weight loss calculator above to explore potential weight loss outcomes at different Mounjaro doses — this can help inform discussions with your prescriber. The dose titration schedule typically starts at 2.5mg, increasing by 2.5mg every 4 weeks until you reach your therapeutic dose or the 15mg maximum. Your prescriber will advise on the right dose escalation pace for you. Storage is straightforward: unopened pens stay in the fridge at 2–8°C until the expiry date; after first use, pens can be kept at room temperature (below 30°C) for up to 30 days. If you miss a dose, inject within 4 days and continue your normal schedule — if more than 4 days have passed, skip that dose and inject on your next scheduled day. Always dispose of used pens safely in a sharps bin.
- 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 know if I'm injecting Mounjaro correctly?
You should feel a click or hear an audible sound when the dose is activated, and the pen should press firmly against your skin for 6 seconds. The dose counter window on the KwikPen will advance after injection, confirming a successful dose. If you're unsure, ask your pharmacist or prescriber to watch your first injection, or contact your GP practice nurse for guidance.
What's the difference between NHS and private Mounjaro access in the UK?
NHS access is free but typically requires a GP referral and specialist assessment with potentially long waiting lists. Private access is faster (1–2 weeks) and doesn't need an NHS referral, but you pay £140–£320/month depending on dose. Both require a clinical assessment to confirm eligibility and safety.
Can I switch between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, while Wegovy (semaglutide) is GLP-1-only — they have different mechanisms and doses. Any switch must be managed by your prescriber, as there is no official established conversion chart. Individual results vary between medications.
What happens if I miss a Mounjaro injection?
If you miss your weekly injection, you can inject within 4 days and return to your normal schedule. If more than 4 days have passed, skip that dose and inject on your next scheduled day. Maintain at least 72 hours (3 days) between injections. Contact your pharmacist or prescriber if you're unsure.
Where should I inject Mounjaro and can I rotate sites?
You can inject into your stomach (abdomen), upper thigh, or upper arm (upper arm requires assistance). Rotate your injection site each week to prevent lipohypertrophy (thickened skin). Always use a clean site and pinch the skin gently during injection to ensure the needle enters fatty tissue, not muscle.
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.