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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Can You Take a Half Dose of Mounjaro from a Kwikpen?
If you're prescribed Mounjaro (tirzepatide), you may wonder whether you can split a Kwikpen to use a half dose. The short answer is: the pens are not designed for splitting, and your prescriber will provide you with a specific starting dose. Mounjaro dosing follows a structured titration schedule in the UK, with each pen containing exactly one week's dose. Here's what you need to know about Mounjaro doses, dose titration, and how the Kwikpen system works.
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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 Mounjaro Kwikpen Dosing Works in the UK
Each Mounjaro Kwikpen is a pre-filled, single-dose injection pen designed to deliver one specific dose over four weeks. The pens come in these strengths: 2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg, and 15 mg. A standard course involves one injection per week, meaning each Kwikpen is used once weekly for four weeks before switching to the next dose.
Mounjaro dose titration in the UK follows this schedule:
- Weeks 1–4: 2.5 mg starting dose
- Weeks 5–8: 5 mg (first escalation)
- Weeks 9–12: 7.5 mg
- Weeks 13–16: 10 mg
- Weeks 17–20: 12.5 mg
- Week 21 onwards: 15 mg maximum dose
Your prescriber will not prescribe a half dose because the titration schedule is designed to allow your body to adjust gradually. If a lower dose is needed, you remain on that dose for the full four weeks before escalating. The Kwikpen itself cannot be accurately split — each pen is calibrated to deliver its full stated dose in a single injection.
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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.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
What If You Need a Different Dose?
If you're experiencing side effects or your prescriber decides you should stay at a lower dose longer, you simply continue with that dose for another cycle (four weeks). You do not split the pen. For example, if you're on 5 mg but want to remain there for eight weeks instead of four, your prescriber will arrange two courses of 5 mg Kwikpens. When comparing weight management options, many UK patients also consider Mounjaro vs Wegovy — both are licensed for weight management but differ in mechanism and dosing. Your GP or prescriber will assess your mounjaro eligibility UK and recommend the most appropriate dose based on your health, weight, and any existing conditions. Always inform your prescriber if you're concerned about side effects or dosing — they can adjust your treatment plan without you needing to split a pen.
- 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.
Can I split a Mounjaro Kwikpen to take half the dose?
No. Mounjaro Kwikpens are pre-filled, single-dose pens designed to deliver a complete, precise dose in one injection. They cannot be split or partially used. If you need a lower dose, your prescriber will prescribe a lower-strength Kwikpen instead, not a partial dose.
What is the starting dose of Mounjaro on NHS prescription?
The standard starting dose is 2.5 mg once weekly for weeks 1–4. After four weeks, you typically escalate to 5 mg. The dose increases gradually every four weeks unless your prescriber advises otherwise. Your mounjaro nhs nice eligibility will be assessed before prescription begins.
How many injections come in one Mounjaro Kwikpen?
Each Kwikpen contains four pre-filled doses — one injection per week for four weeks. After four weeks, you move to the next dose strength and use a new Kwikpen.
What should I do if Mounjaro side effects are too strong?
Contact your prescriber immediately. They may recommend staying on your current dose for an extra cycle before escalating, or switching to a different medication. Never skip doses or attempt to reduce the dose yourself by splitting the pen.
How do I store my Mounjaro Kwikpen?
Unopened pens must be refrigerated at 2–8°C. After first use, you can keep the pen at room temperature (below 30°C) for up to 30 days. Always check the label and discard 30 days after first use, even if medication remains.
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.