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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How Many Clicks Per Pen: Mounjaro vs Wegovy Explained
The Mounjaro KwikPen and Wegovy pen work differently in practice. Mounjaro uses a multi-click dose selection dial system, while Wegovy is a pre-filled single-dose pen. Understanding how each device works helps you prepare for treatment. Both are prescription-only once-weekly injections licensed in the UK for weight management, but the practical administration differs. This guide compares the two and helps you understand which might suit your needs based on clinical assessment.
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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 and Wegovy Pens Work: Key Mechanical Differences
Mounjaro comes in a reusable KwikPen with a dial-based dose selection system. To set your dose, you turn the grey dial until your target dose aligns with the black pointer — each click represents 0.25 mg of tirzepatide. For example, a 5 mg dose requires 20 clicks; a 10 mg dose requires 40 clicks. The pen contains four weeks' worth of doses (four injections). Wegovy, by contrast, uses pre-filled single-dose pens — each pen delivers one fixed dose (0.25 mg, 0.5 mg, 1 mg, 1.7 mg, or 2.4 mg). There is no dialling or clicking; you simply select the pre-filled pen matching your current dose and inject. This practical difference is important: Mounjaro requires you to dial the correct dose each week, while Wegovy requires you to use the correct pre-filled pen for your current dose level.
- Mounjaro: reusable KwikPen, multiple clicks per dose, four weeks per pen
- Wegovy: single-use pre-filled pens, no dose dialling, one pen per 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.
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Mechanism Differences: GLP-1 Only vs Dual GIP+GLP-1 Receptor Activation
The clinical difference between Mounjaro and Wegovy goes beyond the device itself. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two natural hormone pathways simultaneously. Wegovy (semaglutide) is a GLP-1-only receptor agonist — it activates one pathway. In clinical trials, this dual mechanism meant that Mounjaro users experienced slightly greater average weight loss (around 20.9% at the 15 mg dose in SURMOUNT-1) compared to Wegovy users (around 14.9% at 2.4 mg in STEP-1). However, individual results vary considerably, and clinical assessment by a prescriber is essential to determine which is appropriate for you. Both require prescription and are accessed through NHS specialist services or private clinical assessment in the UK.
- 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.
How many times do you click the Mounjaro pen for each dose?
Mounjaro uses a dial system where each 0.25 mg increment equals one click. A 5 mg dose = 20 clicks; 10 mg = 40 clicks; 15 mg = 60 clicks. You turn the grey dial until your target dose aligns with the black pointer on the KwikPen. Always check you've selected the correct dose before injecting.
Is the Mounjaro KwikPen reusable or single-use?
The Mounjaro KwikPen is reusable. Each pen contains four weekly injections (four doses). You dial your dose each week, inject, and keep the pen for the next three weeks until it's empty. After four weeks, you dispose of the pen and start a new one.
How does Wegovy's injection system compare to Mounjaro's?
Wegovy uses single-use pre-filled pens — each pen delivers one fixed dose only. There is no dialling. You select the pre-filled pen matching your current dose level, inject, and dispose of the pen. This is simpler mechanically but generates more pen waste than the reusable Mounjaro system.
Which has better weight loss results in clinical trials: Mounjaro or Wegovy?
In clinical trials, Mounjaro users lost slightly more weight on average (approximately 20.9% at maximum dose) compared to Wegovy users (approximately 14.9% at maximum dose). However, individual results vary significantly. Your prescriber will recommend based on your personal health profile, not trial averages alone.
Can I switch between Mounjaro and Wegovy if one doesn't suit me?
Yes, prescribers can sometimes switch between medications, though this requires clinical assessment. Any switch must be managed by your GP or prescriber — never stop or change medication without guidance. Approximate dose conversions exist, but direct medical advice is essential.
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.