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
How Many Clicks Is 5mg On A 7.5mg Mounjaro Pen?
If you're using a 7.5mg Mounjaro KwikPen and need to administer a 5mg dose, you cannot simply adjust the clicks — each pre-filled pen delivers a fixed, single dose only. A 7.5mg pen contains exactly 7.5mg and is designed to deliver that full amount in one injection. You cannot dial down a higher-dose pen to get a lower dose. If your prescriber has changed your dose from 7.5mg to 5mg, you need a new 5mg pen. This UK health guide explains how Mounjaro pens work and what to do if your dose changes.
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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 Pens Work — Fixed Doses Only
Mounjaro KwikPens are not adjustable dose devices. Unlike some insulin pens, Mounjaro pens are pre-filled with a specific dose and deliver that entire dose in a single injection. Each pen contains one of these doses:
- 2.5mg pen = one 2.5mg injection only
- 5mg pen = one 5mg injection only
- 7.5mg pen = one 7.5mg injection only
- 10mg pen = one 10mg injection only
- 12.5mg pen = one 12.5mg injection only
- 15mg pen = one 15mg injection only
The pen has no dose selector dial. Once you remove the needle cap and inject, the full dose is delivered automatically. There is no way to get 5mg from a 7.5mg pen — the pen is designed to give you exactly 7.5mg, nothing less. If your prescriber reduces your dose, you must obtain a new pen containing the lower dose.
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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 to Do If Your Dose Changes — UK Health Advice
If your GP or prescriber adjusts your Mounjaro dose downwards (for example, from 7.5mg to 5mg), you should not attempt to use the higher-dose pen. Instead, contact the pharmacy or prescriber who supplied your medication and request a new pen with the correct dose. Do not try to inject only part of the contents — this is unsafe and may cause you to receive an incorrect dose. Your prescriber will have adjusted your dose based on your individual response and side effects. Using the wrong dose could affect your health. If you're tracking your weight loss progress, use our free weight loss calculator to monitor projected outcomes at your new dose.
Always follow your prescriber's instructions exactly. If you have questions about your dose or how to use your Mounjaro pen, contact your GP, pharmacist, or the NHS helpline. Never share pens between people — each pen is prescribed for one person only. Store your pens correctly (in the fridge at 2–8°C unopened, or at room temperature below 30°C for up to 30 days after first use). If you lose a pen or need clarification on your dose, ask your prescriber for a replacement before your next scheduled injection date. Keeping track of your weight management journey is easier with our free progress tracker, which helps you monitor changes week by week alongside your medication.
- 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 partially use a 7.5mg Mounjaro pen to get 5mg?
No. Mounjaro pens deliver a fixed, complete dose. A 7.5mg pen cannot be adjusted or partially used — it delivers the full 7.5mg in one injection. If your dose has changed to 5mg, you must obtain a new 5mg pen from your prescriber or pharmacy. Do not attempt to inject only part of the pen's contents.
What if I've been given the wrong dose pen?
Contact your prescriber or pharmacy immediately. Do not use the pen if it's not the dose you've been prescribed. They will arrange a replacement pen with the correct dose. Always check the dose label on your KwikPen matches your prescription before injecting.
How do I know which dose is in my pen?
The dose is printed clearly on the side of the KwikPen box and on the pen itself. It will show "2.5mg", "5mg", "7.5mg", "10mg", "12.5mg", or "15mg". Check this before your injection every time. If the label is unclear or damaged, contact your pharmacy.
What happens if I accidentally use the wrong dose?
Contact your GP or NHS 111 immediately. Tell them which dose you received and when. In most cases, a single incorrect dose is not dangerous, but your prescriber needs to know to adjust your next scheduled dose. Do not inject your next dose until you've spoken to your prescriber.
Can I store a partially used Mounjaro pen for later?
Once a Mounjaro pen has been used, it must be disposed of after 30 days — you cannot reuse it. Do not attempt to store a used pen for a future dose. Each injection uses the entire contents of one pen, which is then discarded.
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.