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 ML in Mounjaro Dose — Comparison with Wegovy
Mounjaro (tirzepatide) comes in pre-filled KwikPen devices, not measured in traditional mL volumes like oral medications. Each pen contains a specific dose of tirzepatide — from 2.5 mg up to 15 mg — delivered as a once-weekly injection. Understanding the actual volume and how this compares to Wegovy (semaglutide) can help clarify what to expect when using this prescription weight management injection. This guide explains Mounjaro dosing, KwikPen volume, and how the two medications differ in practical terms.
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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 Dose Volumes and KwikPen Specifications
Mounjaro does not measure doses in mL — it measures by active ingredient (tirzepatide) in milligrams. Each KwikPen contains 4 pre-filled doses (one month's supply) of a single strength:
- 2.5 mg pen: Approximate volume ~1.5 mL total per pen (4 doses)
- 5 mg pen: Approximate volume ~1.5 mL total per pen
- 7.5 mg pen: Approximate volume ~1.5 mL total per pen
- 10 mg pen: Approximate volume ~1.5 mL total per pen
- 12.5 mg pen: Approximate volume ~1.5 mL total per pen
- 15 mg pen: Approximate volume ~1.5 mL total per pen
The actual volume delivered per injection is approximately 0.375 mL (less than 0.5 mL), regardless of the dose strength. This is much smaller than oral medications and allows for precise, easy self-injection once weekly using the automatic KwikPen device.
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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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Mounjaro vs Wegovy — Dosing and Delivery Differences
Wegovy (semaglutide) also uses pre-filled pens but operates differently. Wegovy doses range from 0.25 mg to 2.4 mg, and like Mounjaro, the actual injection volume is minimal (under 0.5 mL per injection). Both medications are prescription-only and require a clinical assessment before being prescribed. The choice between Mounjaro and Wegovy depends on individual health factors, not on injection volume — your prescriber will assess which mechanism (dual GIP+GLP-1 for Mounjaro, or GLP-1 only for Wegovy) suits your needs. Use our free GLP-1 weight loss calculator to understand projected outcomes at different dose levels, and try the BMI calculator to check your starting point.
- 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.
What does mL mean on a syringe, and does Mounjaro come in mL doses?
mL stands for millilitre — a unit of volume. Mounjaro does not come in mL doses. Instead, it's dosed by the amount of active ingredient (tirzepatide) in milligrams. Each KwikPen contains approximately 1.5 mL total volume across 4 weekly doses, but you don't measure or choose by mL — your GP or prescriber determines your dose in mg.
Is Mounjaro injection volume painful or difficult to self-inject?
No. The actual volume injected is very small — approximately 0.375 mL per injection. The KwikPen is designed for easy, automatic self-injection under the skin. Most users find it quick and relatively painless. Injection site reactions are common but usually mild (redness, bruising).
Can I store a Mounjaro KwikPen in a syringe or transfer it to a different container?
No. Mounjaro must be stored and used in its original KwikPen device. Do not attempt to transfer the medicine. Unopened pens store in the fridge at 2–8°C. After first use, a pen can be kept at room temperature (below 30°C) for up to 30 days.
How does Mounjaro's dose volume compare to Wegovy?
Both medications deliver less than 0.5 mL per injection. Mounjaro ranges from 2.5 mg to 15 mg once weekly; Wegovy ranges from 0.25 mg to 2.4 mg once weekly. The actual injection volumes are similar and very small. The main difference is the active ingredient and mechanism — Mounjaro is a dual GIP+GLP-1 agonist; Wegovy is GLP-1 only.
What should I do if I accidentally inject less than the full dose from a KwikPen?
Contact your GP or prescriber immediately for advice. Do not attempt to inject again from the same pen. The KwikPen is designed to deliver the full dose automatically — if you're unsure whether a dose was delivered, seek medical guidance before your next injection. Do not skip the dose or double up.
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