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
Does a Mounjaro Pen Contain an Extra Dose?
Each Mounjaro KwikPen is pre-filled with exactly four doses of tirzepatide—one dose per week for four weeks. There is no extra dose built into the pen design. Understanding how your Mounjaro kwikpen works is essential for safe, correct use. Your prescriber will guide you through the injection process, and the pen is designed to deliver one precise dose when you press the button each week. If you have concerns about whether you've received the correct dose or whether your pen is functioning properly, always contact your GP or the pharmacy that dispensed your medication.
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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.
How Mounjaro KwikPen Doses Are Managed
Each Mounjaro KwikPen contains exactly four pre-measured doses. The pen is a pre-filled, disposable device—you cannot extract additional doses or adjust the amount. Once you've completed all four doses (one per week), the pen is empty and must be disposed of safely in a sharps bin.
- Weeks 1–4: First pen contains doses for the initial four weeks
- Weeks 5–8: Second pen arrives (if your prescriber continues treatment)
- Dose titration follows a set schedule—your dose may increase every 4 weeks, but only as prescribed by your GP or specialist
- Each dose is locked into the pen by design—you receive the exact mg your prescriber specified
The KwikPen design prevents accidental overdosing or underdosing. If you have questions about your specific dose during mounjaro dose titration, speak with your prescriber before your next injection.
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.
Cost, Access, and Getting Mounjaro in the UK
Mounjaro is available in the UK through NHS specialist services or private prescription. On the NHS, access depends on your BMI, health conditions, and regional availability—referral to a tier 3 weight management service is typically required, and waiting lists vary considerably by area.
For private access, you can obtain a prescription following an online clinical assessment with a UK-licensed prescriber. Private cost varies by dose and provider, typically ranging from £120–£300+ per month. Your prescriber will assess your mounjaro nhs nice eligibility and discuss whether you qualify for treatment. Use our GLP-1 weight loss calculator to explore potential outcomes, and discuss all options with your GP before proceeding.
- 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 get extra doses from a single Mounjaro pen?
No. Each KwikPen contains exactly four pre-filled doses—one per week. The pen design does not allow extraction of additional doses. Once you've used all four doses, the pen must be disposed of safely in a sharps bin. Your next four-week supply arrives as a separate pen.
What if I think my Mounjaro pen is faulty or has not delivered a full dose?
Contact your pharmacy or GP immediately. Do not attempt to use the pen again if you suspect a problem. Your prescriber may arrange a replacement pen or dose adjustment. Never try to extract doses manually from a KwikPen—this is unsafe and will damage the device.
How does Mounjaro dose titration work in the UK?
Your prescriber starts you on 2.5mg and may increase your dose every 4 weeks, following a set schedule up to a maximum of 15mg weekly. Each increase is based on your response and tolerability. You receive a new pen every four weeks—each pen is pre-filled with your current prescribed dose.
Is Mounjaro available on the NHS, or do I need to pay privately?
Both options exist in the UK. NHS access is through specialist tier 3 weight management services—eligibility depends on BMI and health conditions, with regional variation. Private access is faster, available following an online clinical assessment with a UK-licensed prescriber, typically costing £120–£300+ per month depending on dose.
How does tirzepatide in Mounjaro compare to other weight loss injections like Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, whereas Wegovy (semaglutide) is a GLP-1 agonist only. Clinical trials showed tirzepatide resulted in slightly higher average weight loss (~15–21% body weight), but individual results vary significantly. Both are prescription-only and require clinical assessment before 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.