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 Use Your Mounjaro Kwikpen 2.5 mg Injection
Mounjaro Kwikpen 2.5 mg is the starting dose of tirzepatide, a prescription-only weight management injection available in the UK. This informational guide explains the step-by-step process for using your Kwikpen device safely and correctly. The 2.5 mg dose is designed as an initial adjustment dose, typically used for the first four weeks before your prescriber may increase the dose. Understanding the correct injection technique helps ensure you get the most from your treatment, and this guide covers storage, preparation, injection sites, and what happens after your injection.
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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.
Step-by-Step Injection Instructions for Mounjaro Kwikpen
Before you inject: Remove your Kwikpen from the fridge and let it sit at room temperature for 15–30 minutes — this makes the injection more comfortable. Check the insulin inside the pen window; it should be clear and colourless. If it's cloudy or discoloured, do not use it. Wash your hands thoroughly with soap and water.
Preparing the injection: Hold the Kwikpen upright with the cap on. Twist the cap off (do not pull). Select your dose by turning the dose selector until 2.5 appears in the dose window. A click will confirm the dose is set. Wipe your chosen injection site with an alcohol swab and let it dry fully.
Injecting: Pinch the skin at your chosen site and insert the needle at 90 degrees (straight in). Press the injection button until you hear a click and feel a second click approximately 3–5 seconds later — this confirms the full dose has been delivered. Count to 6 after the second click, then withdraw the needle. Release the pinched skin. You may see a small amount of blood or clear fluid — this is normal.
After injection: Place the used pen in a sharps bin. Do not recap the needle.
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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 Injection Sites and Storage Information
Where to inject: You can inject Mounjaro into your stomach (abdomen), upper thigh, or upper arm. Rotate your injection site each week — if you injected your stomach last week, choose your thigh this week. This reduces the risk of skin irritation or lumps at injection sites. Each site should be at least 2.5 cm away from your previous injection.
Storage and shelf life: Unopened Kwikpens must be stored in a fridge at 2–8°C in their original carton to protect from light. Do not freeze them. Once you start using a pen, it can stay at room temperature (below 30°C) for up to 30 days. After 30 days, discard the pen even if insulin remains. Keep your spare pens refrigerated. If your pen has been frozen, do not use it.
Missed dose: If you miss your weekly injection, take it as soon as you remember if it is within 4 days of the scheduled time. If more than 4 days have passed, skip that dose and inject on your normal scheduled day. Maintain at least 3 days (72 hours) between injections.
- 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 2.5 mg hurt when you inject it?
Most people find the Mounjaro injection minimally painful. The needle is very fine (29 gauge). Letting the pen warm to room temperature for 15–30 minutes before injection, pinching the skin firmly, and injecting slowly can all reduce discomfort. Some people feel only a slight pressure. If you experience pain during injection, you may have hit a nerve — try a different injection site next time.
How long does a Mounjaro Kwikpen last?
Each Kwikpen contains four weekly doses. At 2.5 mg once per week, one pen lasts exactly four weeks. You will need a new pen each month. If you store your pen correctly in the fridge, it remains usable until the expiry date printed on the box. Once opened, discard after 30 days even if insulin remains.
Can you travel with Mounjaro Kwikpen?
Yes, you can travel with Mounjaro, but it requires careful planning. Inform airport security in advance. Keep your prescription or a letter from your prescriber with you. Transport your pens in an insulated travel case with cooling packs to maintain the 2–8°C temperature. Do not check your Kwikpen in checked luggage; keep it in your carry-on bag where you can monitor temperature control throughout your journey.
What happens if you accidentally inject twice in the same week?
If you inject twice within one week by mistake, contact your GP or pharmacist for guidance immediately. Do not inject again until your scheduled injection day. Taking the dose twice increases the risk of side effects such as severe nausea or vomiting. Your prescriber may advise you to skip the next injection or adjust your schedule — do not self-manage this without professional advice.
Is Mounjaro Kwikpen available on the NHS in the UK?
Mounjaro (tirzepatide) has been approved by NICE for NHS use in specialist weight management services (tier 3). However, NHS availability is limited and varies significantly by region. Most people in the UK access Mounjaro through private online prescribing following a clinical assessment with a UK-licensed prescriber. Ask your GP if your local NHS service offers this medication, as waiting lists can be very lengthy in many areas.
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