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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Monjaro Pens — Complete UK Guide
Monjaro is delivered via a pre-filled injection pen called the KwikPen, a once-weekly GLP-1 and GIP receptor agonist approved for weight management in UK adults. This guide explains how Monjaro pens work, the available doses, storage requirements, and how to access them in the UK. Always consult your GP or a qualified healthcare professional before starting any weight loss treatment.
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Calculate Your BMI Instantly
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 Monjaro KwikPen Works
Monjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — this dual mechanism is what differentiates it from other weight loss injections like Wegovy (semaglutide), which targets GLP-1 alone. The KwikPen delivers a pre-measured dose subcutaneously (under the skin) once weekly.
- Each KwikPen contains 4 doses, providing a 4-week supply
- Pens are colour-coded by dose strength for easy identification
- The injection takes just a few seconds and can be self-administered at home
- Injection sites include the stomach (abdomen), upper thigh, or upper arm
The dual action helps regulate appetite, reduce food cravings, and support feeling fuller after smaller meals. Clinical trials showed participants using Mounjaro lost an average of 15–21% of their body weight — individual results vary significantly.
Clinically BackedWeight Loss
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.
Monjaro Pen Storage & Handling
Unopened pens must be stored in a refrigerator at 2–8°C and must not be frozen. Keep pens in their original carton to protect from light, and they can be used until the expiry date if stored correctly. After first use, pens can be kept at room temperature (below 30°C) for up to 30 days. Always check the pen before injection — if it looks cloudy, discoloured, or damaged, do not use it. Dispose of used pens according to NHS guidance, typically in a sharps bin provided by your pharmacy or GP practice.
Monjaro is prescription-only in the UK and requires a clinical assessment before being prescribed. Access is available through NHS specialist weight management services (typically tier 3 services) or private online prescribing via a licensed prescriber. Use our free GLP-1 weight loss calculator to estimate potential weight loss at different doses. Your prescriber will assess your BMI, health conditions, and medications to determine suitability. Calculate your starting point with our free BMI calculator to understand where you sit on NHS guidelines.
- 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 is a Monjaro pen exactly?
A Monjaro pen (KwikPen) is a pre-filled, single-use injection device containing tirzepatide. Each pen delivers one weekly dose. Four pens are supplied together (4-week supply). The pen is colour-coded by dose strength and is designed for self-injection at home.
How do I inject Monjaro from the pen?
Remove the pen from the refrigerator 15 minutes before use. Clean your chosen injection site with an alcohol wipe. Pinch the skin, insert the needle at a 90-degree angle, and press the injection button until you hear a click. Hold for 3 seconds, then withdraw. Your GP or pharmacist can demonstrate the correct technique.
Can I reuse a Monjaro pen?
No. Each Monjaro KwikPen is single-use and contains exactly one dose. Once you've injected, the pen is disposed of. Do not attempt to reuse pens — they are designed for one injection only and cannot be refilled.
What if I miss a Monjaro injection?
If you remember within 4 days of the missed dose, take it as soon as you can and continue your normal schedule the following week. If more than 4 days have passed, skip that dose and take your next dose on your regular scheduled day. Never take a double dose.
Where can I get Monjaro pens in the UK?
Monjaro is available through NHS specialist weight management services (referral required from your GP) or private online prescribing. Private prescriptions are dispensed by GPhC-registered pharmacies. Costs and waiting times vary — your GP or prescriber can advise on the best route for you.
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.