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 On A Mounjaro Pen?
The Mounjaro KwikPen doesn't use numbered clicks like some other injection devices — instead, it features a single-button press mechanism that delivers the full dose in one injection. This is different from some older-style pens that require multiple clicks to set and deliver doses. Understanding how the Mounjaro pen works, and how it compares to the Wegovy auto-injector, can help you feel more confident using these tirzepatide and semaglutide weight loss injections in the UK. Both are prescription-only medicines requiring clinical assessment before use.
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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.
Mounjaro KwikPen vs Wegovy Auto-Injector: How They Work
Mounjaro KwikPen injection mechanism: The Mounjaro pen is a pre-filled, single-use KwikPen device that delivers your full weekly dose with one button press. There are no numbered clicks to set the dose — the dose is pre-set at the factory (2.5mg, 5mg, 7.5mg, 10mg, 12.5mg, or 15mg) based on your prescription. You simply remove the cap, place it against your skin (abdomen, thigh, or upper arm), press the button once, hold it in place for several seconds, and the needle automatically retracts. Each pen contains exactly one dose for one week.
Wegovy auto-injector: Wegovy uses a similar pre-filled auto-injector pen system, but the doses progress differently — starting at 0.25mg and advancing through 0.5mg, 1mg, 1.7mg, and up to 2.4mg maximum. Like Mounjaro, Wegovy doses are pre-set at the factory, so no a UK pharmacy clicking or dialling is required. The injection mechanism is also single-button activated with automatic needle retraction.
Key difference: Mounjaro is a dual GIP and GLP-1 receptor agonist, whereas Wegovy is a GLP-1 receptor agonist only. This affects how they work in your body, not how the pens function — both deliver their dose with a simple one-button press.
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.
Dosing and Storage: What You Need to Know
Both Mounjaro and Wegovy use once-weekly dosing — you inject the same dose every 7 days on your chosen day. Your prescriber will start you on a lower dose and gradually increase it every 4 weeks if needed, based on tolerability and response. Each Mounjaro pen contains one week's dose (one 2.5mg, 5mg, 7.5mg, 10mg, 12.5mg, or 15mg injection), so you dispose of it after use. Unopened pens should be stored in a refrigerator at 2–8°C, but after first use they can be kept at room temperature (below 30°C) for up to 30 days. Always check the expiry date on your pen before injection, and ask your prescriber or pharmacist if you're unsure about injection technique or storage.
- 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.
Does Mounjaro require multiple clicks like older insulin pens?
No. Mounjaro KwikPen delivers the entire dose with a single button press. The dose is pre-set at the factory, so there's no dialling or clicking needed. Just press once and hold for several seconds — the needle retracts automatically.
How is Mounjaro dosing different from Wegovy?
Mounjaro uses larger doses (2.5mg to 15mg once weekly) and is a dual GIP and GLP-1 agonist. Wegovy uses smaller doses (0.25mg to 2.4mg once weekly) and is a GLP-1 agonist only. Both start low and increase gradually; both use once-weekly injection schedules.
Can I reuse a Mounjaro KwikPen?
No. Each Mounjaro pen is single-use only and contains exactly one week's dose. After your injection, dispose of it safely in a sharps bin. You'll receive a new pen each week as part of your prescription supply.
What's the main advantage of the KwikPen design?
The KwikPen design is simple and user-friendly — one button press delivers the full dose automatically. There's no risk of miscounting clicks or accidentally underdosing, and the automatic needle retraction makes it safer and less intimidating for first-time users.
Do I need clinical assessment before starting Mounjaro in the UK?
Yes. Mounjaro is prescription-only in the UK. You'll need a clinical assessment from a qualified prescriber to check whether it's suitable for you based on your BMI, health conditions, medications, and medical history. Access is through NHS specialist services or private online prescribing.
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.