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
Free tracker included with every download this week
How To Do The Mounjaro Injection At Home
If you've been prescribed Mounjaro (tirzepatide) as a weight loss injection, you'll be administering it yourself at home using the pre-filled KwikPen device. This straightforward once-weekly injection is designed to be easy to use, but understanding the correct technique ensures you get the most from your treatment. This guide walks you through each step, from preparation through to safe disposal, so you can inject with confidence. Always follow the specific instructions provided by your prescriber and the patient information leaflet included with your medication.
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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.
Preparing And Administering Your Mounjaro KwikPen
Before you inject: Remove your Mounjaro KwikPen from the fridge and let it reach room temperature for 15–30 minutes — this makes the injection less uncomfortable. Wash your hands thoroughly with soap and water. Gather your supplies: alcohol wipe, cotton wool or gauze pad, and a sharps disposal container.
Choosing an injection site: Mounjaro is injected into the fatty tissue (subcutaneously) on your stomach, upper thigh, or upper arm. Rotate your injection site each week to prevent skin irritation and lipohypertrophy (thickened patches of skin). If injecting into your upper arm, ask a family member or healthcare professional to help.
Preparing the site: Wipe the injection site with an alcohol wipe and allow it to air dry completely — do not blow on it or fan it. Remove the grey and blue caps from your KwikPen. You do not need to remove the needle cover yet.
Setting your dose: Align the dose selector with your prescribed dose (2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg, or 15 mg). You'll hear a clicking sound as you turn the dial. Double-check the dose window to confirm the correct dose is selected.
Injecting: Remove the needle cover by twisting it off. Pinch the skin at your injection site, insert the needle at a 90-degree angle, and press the injection button down slowly and firmly until it stops. Keep the button pressed for 3 seconds to ensure the full dose is delivered. Remove the needle and release the pinched skin. Do not rub the injection site — instead, apply gentle pressure with a clean cloth if needed.
After injection: Replace the blue cap on your KwikPen and store it in the fridge (2–8°C). Dispose of the needle safely in your sharps container.
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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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Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Common Injection Concerns And Practical Tips
If you experience discomfort, this usually improves after the first few injections as your body adjusts. Pain or burning at the injection site is common but should be mild. If you experience severe pain, bruising that does not resolve, or signs of infection (redness, warmth, pus), contact your GP immediately.
Missed doses: If you miss your weekly injection, take it within 4 days of your scheduled day and return to your normal schedule. If more than 4 days have passed, skip that dose and inject on your next scheduled day — never inject twice in one week. Ensure at least 3 days passes between doses.
Storage after first use: Once you've started using a KwikPen, you can store it at room temperature (below 30°C) for up to 30 days. After 30 days from first use, discard the pen even if it contains remaining medication. Keep it away from heat and direct sunlight. Never freeze your Mounjaro — if frozen, discard it immediately.
Track your weight loss progress using our free progress tracker to monitor how the injection is working alongside your reduced-calorie diet and increased physical activity. Our GLP-1 weight loss calculator can also help you understand potential outcomes based on your current weight and dose.
- 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.
Does Mounjaro injection hurt?
Most people experience only minor discomfort or stinging during or after the injection. Pain usually decreases after the first few injections. If pain is severe or lasts longer than a few hours, contact your GP. Using room-temperature medication, allowing the injection site to dry, and rotating sites each week can all help reduce discomfort.
What happens if I inject Mounjaro incorrectly?
If you suspect you've injected incorrectly, contact your prescriber or NHS 111 for guidance. Common errors (like injecting too quickly or at the wrong angle) may result in incomplete dose delivery or increased discomfort, but they're rarely dangerous. Do not try to re-inject on the same day — wait until your next scheduled injection.
Can I reuse a Mounjaro needle?
No — each needle is designed for single use only. Reusing needles increases infection risk, causes blunting which makes injection more painful, and may result in incomplete dose delivery. Always use a new needle for each weekly injection.
What should I do with my used KwikPen?
Dispose of needles in a sharps container designed for medical waste. Once a KwikPen is empty or 30 days have passed since first use, place the entire pen in your sharps container. Never put sharps in household waste. Your pharmacy or GP surgery can advise on local sharps disposal collection points.
Is Mounjaro injection different from Wegovy injection?
Yes — Mounjaro (tirzepatide) is a dual GIP and GLP-1 injection once weekly, whilst Wegovy (semaglutide) is a GLP-1 injection also once weekly. Both use pre-filled pens, but Mounjaro's KwikPen design and dose range (2.5–15 mg) differ from Wegovy's. Your prescriber will determine which medication is appropriate for you.
Ready to take control of your weight loss journey?
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