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 Per Dose: Mounjaro vs Wegovy
Mounjaro and Wegovy are both once-weekly weight loss injections available in the UK, but they come in different concentrations. Mounjaro contains tirzepatide and uses a dual GIP and GLP-1 mechanism, whilst Wegovy contains semaglutide and works via GLP-1 only. Understanding the ml volume of each dose, how the KwikPen works, and how they differ can help you and your prescriber decide which is right for you. Both require a UK prescription following 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.
Mounjaro Dosing: Volume, Strength, and Titration Schedule
Mounjaro doses are pre-filled into a KwikPen auto-injector device. Each pen contains 4 weekly doses and delivers a fixed volume based on the dose strength:
- 2.5 mg dose: delivers 0.25 ml of solution
- 5 mg dose: delivers 0.5 ml of solution
- 7.5 mg dose: delivers 0.75 ml of solution
- 10 mg dose: delivers 1 ml of solution
- 12.5 mg dose: delivers 1.25 ml of solution
- 15 mg dose: delivers 1.5 ml of solution
Mounjaro uses dose titration, meaning you start at 2.5 mg and increase every 4 weeks if tolerated, up to the maximum of 15 mg. Each KwikPen lasts 4 weeks. The ml volume increases proportionally with the dose strength. You inject once weekly, always on the same day.
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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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Wegovy Dosing: How It Compares to Mounjaro
Wegovy also comes in a pre-filled auto-injector pen but uses different dose strengths and volumes. Starting doses begin at 0.25 mg and escalate to a maximum of 2.4 mg over approximately 4 months. Each Wegovy dose is smaller in absolute mg terms, and the injection volume is correspondingly smaller. The GLP-1 mechanism in Wegovy is single-pathway (compared to Mounjaro's dual GIP and GLP-1 action), which may explain why escalation is slower and maximum dose is lower. Both medications show similar average weight loss in clinical trials — approximately 14–21% of body weight — though individual results vary significantly. Your prescriber will assess which is suitable based on your health history and preferences.
- 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 you feel the difference between a 2.5 mg and 15 mg Mounjaro injection?
The ml volume difference is small (0.25 ml vs 1.5 ml), so the physical sensation may not vary dramatically. However, side effects like nausea and appetite suppression typically increase with higher doses. Many people report stronger appetite suppression at 10 mg and above.
Why is Mounjaro measured in mg, not ml?
Prescription medications are dosed by active ingredient strength (mg), not volume (ml). This ensures you receive the correct therapeutic dose regardless of how the solution is formulated. The ml is simply how much liquid the KwikPen injects.
Is Mounjaro stronger than Wegovy because the ml volumes are larger?
No — Mounjaro's maximum dose is 15 mg (1.5 ml), whilst Wegovy's maximum is 2.4 mg. They are different medications with different mechanisms. Clinical trials show similar average weight loss (~15–20%), but individual results vary. A prescriber will decide which suits you.
Can you use a Mounjaro KwikPen multiple times?
No. Each KwikPen contains exactly 4 doses (one per week for 4 weeks). Once empty, you dispose of it safely and obtain a new pen for the next month. Do not attempt to reuse or refill pens.
Where should I store my Mounjaro KwikPen?
Unopened pens go in the fridge at 2–8°C. After first use, you can store at room temperature (below 30°C) for up to 30 days. Never freeze. Keep in the original carton away from light and heat.
Ready to take control of your weight loss journey?
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