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 In A Mounjaro Pen?
A Mounjaro KwikPen doesn't use traditional "clicks" — instead, each pen contains 4 pre-measured doses that you inject once weekly. Unlike some older injection devices, the Mounjaro pen has a straightforward mechanism: twist the dose selector to your prescribed dose, inject, and the pen automatically dispenses the correct amount of tirzepatide. Understanding how your weight loss injection pen works is important for confidence and safety with any prescription medication.
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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.
Mounjaro KwikPen vs Wegovy Pen: How They Work
Mounjaro (tirzepatide) uses a KwikPen device with a twist-to-select mechanism. Each pen holds 4 weekly doses, so you get a 4-week supply per pen. The doses available are 2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg, and 15 mg — you select your prescribed dose by twisting the dial to the number, then inject. There are no "clicks" in the traditional sense; instead, the pen has a simple dial selector.
Wegovy (semaglutide) also comes in a pre-filled auto-injection pen but uses a different delivery system. Wegovy pens contain a single dose and come in doses of 0.25 mg, 0.5 mg, 1 mg, 1.7 mg, and 2.4 mg. Each pen is single-use — once you've injected, you dispose of that pen and use a new one for your next weekly injection. This means Wegovy requires more individual pens over a treatment course compared to the Mounjaro KwikPen's 4-dose cartridge approach.
Both are prescription-only medicines requiring clinical assessment before being prescribed. Your GP or licensed prescriber will assess your eligibility based on your BMI, health conditions, and individual circumstances. The choice between Mounjaro and Wegovy depends on what your prescriber recommends for you.
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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.
Dose Titration: How Both Medications Escalate
Both Mounjaro and Wegovy follow a dose titration schedule — meaning you start at a low dose and gradually increase it every 4 weeks. With Mounjaro dose titration, you begin at 2.5 mg for weeks 1–4, then increase to 5 mg for weeks 5–8, continuing upwards to a maximum of 15 mg. With Wegovy, you start at 0.25 mg, increase to 0.5 mg in week 5, then 1 mg, 1.7 mg, and finally 2.4 mg. Clinical trials (SURMOUNT for Mounjaro, STEP for Wegovy) showed that higher doses produced greater average weight loss, though individual results vary significantly. Both require a prescription and ongoing support from your healthcare provider to ensure the dose is right for you.
- 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 pen have clicks like older insulin pens?
No. The Mounjaro KwikPen uses a twist-to-select dial mechanism, not a clicking system. You twist the dial to your prescribed dose number, then inject. The pen holds 4 weekly doses, so each KwikPen lasts 4 weeks before disposal.
How many pens do I need for Mounjaro treatment?
Each KwikPen contains 4 weeks of doses. If you're on treatment for 12 weeks, you'll need 3 pens. If you're increasing doses every 4 weeks, you may need multiple pens as you progress through the dose titration schedule.
Is Wegovy pen easier to use than Mounjaro?
Both are user-friendly, but they work differently. Wegovy uses single-dose pens (one pen per week), while Mounjaro's KwikPen holds 4 doses. Neither is objectively "easier" — it depends on personal preference and what your prescriber recommends.
Can I switch between Mounjaro and Wegovy mid-treatment?
Any switch between medications must be managed by your prescriber. Mounjaro is a dual GIP/GLP-1 agonist while Wegovy is GLP-1 only — they work differently. Your GP or prescriber will advise if switching is appropriate for you.
Where should I inject Mounjaro or Wegovy?
Both can be injected into the stomach (abdomen), upper thigh, or upper arm. Rotate injection sites each week to prevent irritation. Your prescriber will show you the correct injection technique before you start treatment.
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.