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
What Is a Kwik Pen? UK Health Guide
A Kwik Pen is the pre-filled injection device used to deliver Mounjaro (tirzepatide), a prescription-only weight management medication available in the UK. It's a convenient, once-weekly self-injection pen designed for adults who have been prescribed Mounjaro by their GP or a licensed prescriber following clinical assessment. This health guide explains how the Kwik Pen works, storage requirements, and how to access this medication within the UK healthcare system.
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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.
How the Mounjaro Kwik Pen Works in Practice
The Kwik Pen is a pre-filled, single-use injection device that delivers a fixed dose of Mounjaro (tirzepatide) once per week. Each pen contains enough medication for one weekly dose and is designed to be simple and discreet to use.
- Dose range: Kwik Pens are available in doses from 2.5 mg up to 15 mg, depending on your individual treatment plan
- Injection sites: You can inject into your stomach (abdomen), upper thigh, or upper arm — rotating injection sites each week helps prevent skin irritation
- Prescription-only: The Kwik Pen is available only with a valid prescription from a UK-licensed prescriber following a clinical assessment of your suitability
- Once-weekly: One injection per week on the same day each week is the standard schedule — consistency helps your body adjust to the medication
The pen has a small needle and is quick to use — most people take just a few seconds to complete their weekly injection at home.
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No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
UK Storage, Disposal, and Access Information
Storage before use: Unopened Kwik Pens must be kept in a refrigerator between 2°C and 8°C and should never be frozen. Each pen has an expiry date printed on the carton. After first use: Once you've started using a pen, it can be stored at room temperature (below 30°C) for up to 30 days. Always keep pens away from direct sunlight and heat.
UK prescription access: Mounjaro Kwik Pens are available through NHS specialist weight management services (tier 3) or through private online prescribing with a UK-licensed prescriber. Use our free BMI calculator and weight converter to understand your starting point, then consult your GP about whether specialist weight management referral or private assessment is appropriate for you.
- 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 a Kwik Pen and other Mounjaro devices?
The Kwik Pen is the standard pre-filled injection device for Mounjaro in the UK. Each pen is pre-loaded with a single dose and is disposable after use. It's designed for simplicity and convenience compared to multi-dose vials that require separate needles.
Can I use a Kwik Pen if I'm not comfortable with injections?
If you have needle anxiety, speak to your GP or prescriber before starting. They can discuss alternative weight management approaches, provide injection training, or help you manage anxiety around self-injection.
How do I know which Kwik Pen dose I need?
Your prescriber will determine your starting dose (usually 2.5 mg) and increase it gradually over weeks based on your response and tolerability. You cannot choose your own dose — it must be prescribed.
Can I buy Kwik Pens without a prescription in the UK?
No. Mounjaro is prescription-only in the UK. You must have a valid prescription from a GP or licensed prescriber. Private online prescribers can assess your suitability following an online consultation.
What should I do if I miss a weekly Kwik Pen injection?
If you remember within 4 days of your 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 double-dose.
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.