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 Mounjaro Kwikpen 2.5mg — Step-by-Step Guide
The Mounjaro Kwikpen is a pre-filled injection device containing tirzepatide, a dual GIP and GLP-1 receptor agonist for weight management. The 2.5mg dose is the starting point for most people in the UK. This guide explains how to use the Kwikpen safely, how it works, and how it compares to Wegovy, another popular weight loss injection. Always follow your prescriber's instructions and read the patient information leaflet before using any medication.
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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.
Using the Mounjaro Kwikpen 2.5mg — Storage and Injection Steps
Storage: Keep unopened Mounjaro pens in the fridge at 2–8°C in the original carton. Once you start using a pen, you can keep it at room temperature (below 30°C) for up to 30 days. Never freeze the pen.
Before injecting: Remove the pen from storage, check the liquid is clear (not cloudy), and let it reach room temperature if refrigerated (around 15 minutes). Select your injection site: stomach, upper thigh, or upper arm. Rotate sites each week to avoid irritation.
Injection technique: Clean the skin with an alcohol wipe. Pinch the skin gently, insert the needle at 90 degrees, and press the injection button until you hear a click. Keep the needle in skin for 3 seconds after the click. Remove and dispose in a sharps bin. Never reuse needles.
- Inject once weekly on the same day each week
- Each Kwikpen contains 4 doses (4 weeks supply)
- Dispose of pen after 30 days from first use, even if it still has medication
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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 vs Wegovy — Key Differences at Starting Dose
Both Mounjaro and Wegovy are prescription-only weight loss injections available in the UK, but they work differently. Mounjaro's mechanism: The 2.5mg starting dose is a dual GIP and GLP-1 receptor agonist—it activates two hormone pathways simultaneously, which may explain why clinical trials (SURMOUNT-1) showed approximately 15% average body weight loss. Wegovy's mechanism: The 0.25mg starting dose is a GLP-1-only agonist, and STEP-1 trials showed approximately 14.9% average weight loss at the maximum dose.
Both require a prescription following a clinical assessment by a UK-licensed prescriber. Individual results vary significantly. Your GP or prescriber can advise which option is more suitable for your health profile. Use our GLP-1 weight loss calculator to explore potential outcomes, and our BMI calculator to assess your current health status.
- 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.
What's the difference between Mounjaro Kwikpen and Wegovy pen?
Mounjaro contains tirzepatide (dual GIP+GLP-1 agonist) and Wegovy contains semaglutide (GLP-1 only). Mounjaro starts at 2.5mg, Wegovy at 0.25mg. Both are once-weekly injections. Mounjaro pens are used for 4 weeks (4 doses per pen), while Wegovy pens also provide 4 weekly injections. Clinical trials show similar weight loss averages, but individual results vary.
How long does a Mounjaro 2.5mg Kwikpen last?
Each Mounjaro Kwikpen contains 4 pre-filled doses, so one pen lasts 4 weeks if you inject once weekly. You must dispose of the pen after 30 days from first use, even if medication remains. After 30 days, the medication quality cannot be assured.
Can I switch from Mounjaro to Wegovy?
Switching between Mounjaro and Wegovy should only be done under your prescriber's guidance. There is no official conversion chart, but approximate equivalences exist (5mg Mounjaro ≈ 0.5mg Wegovy, 15mg ≈ 2.4mg Wegovy). Your prescriber will manage any transition and monitor your response.
What if I miss a Mounjaro 2.5mg injection?
If you remember within 4 days of the missed dose, inject as soon as you remember and continue your normal weekly schedule. If more than 4 days have passed, skip that dose and inject on your normal scheduled day. Never take two doses to make up for a missed one.
Is Mounjaro available on the NHS in the UK?
NICE has approved tirzepatide (Mounjaro) for NHS specialist weight management services, but availability varies significantly by region. Access is typically through tier 3 specialist services, not standard GP prescriptions. Private prescribing via UK-licensed online services offers quicker access following a clinical assessment.
Ready to take control of your weight loss journey?
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