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 mls in a Mounjaro Dose — UK Comparison
Mounjaro doses contain between 2.5 mg and 15 mg of tirzepatide per weekly injection, delivered in a pre-filled KwikPen device. The exact volume in mls varies slightly by dose, but each pen contains a single 4-week supply. If you're comparing Mounjaro to Wegovy or trying to understand how dosing works before speaking to your prescriber, this guide explains the key differences and how clinical trials showed different outcomes between these two injection-based weight management options.
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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 Dose Volume and Mechanism
Mounjaro (tirzepatide) is supplied as a pre-filled KwikPen auto-injector. The pen delivers a fixed dose once weekly, and the volume in mls is standardised by the manufacturer. Each dose — from 2.5 mg up to the maximum 15 mg — is contained within the same pen design, so the actual ml volume per injection remains consistent across all dose strengths.
The key difference between Mounjaro and Wegovy lies in their mechanism: Mounjaro is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways. Wegovy (semaglutide), by contrast, is a GLP-1 receptor agonist only — it activates a single pathway. Clinical trials (SURMOUNT for Mounjaro, STEP for Wegovy) showed that at their maximum doses, both medications supported average weight loss of around 15–21% body weight, though individual results vary significantly.
- Mounjaro: dual mechanism, once-weekly injection, starting dose 2.5 mg, maximum 15 mg
- Wegovy: single mechanism, once-weekly injection, starting dose 0.25 mg, maximum 2.4 mg
- Both require clinical assessment and are prescription-only in the UK
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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.
Which Medication Is Right for You?
Neither Mounjaro nor Wegovy is universally "better" — suitability depends entirely on your individual health profile, medical history, and what your prescriber assesses as most appropriate. Both are licensed in the UK for adults with a BMI of 30 or above, or BMI of 27–29.9 with weight-related health conditions. Your prescriber will consider factors like your current medications, any previous experience with GLP-1 therapy, tolerance to side effects, and your overall health context.
You can estimate your personal BMI using our free BMI calculator, which gives you a baseline before discussing weight management options with your GP or a licensed prescriber. Both Mounjaro and Wegovy are prescription-only and require a clinical assessment — they are not available over the counter and are typically prescribed following specialist assessment or private online consultation with a UK-licensed prescriber.
- 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 volume in mls is a standard Mounjaro dose?
Each Mounjaro KwikPen delivers a fixed weekly dose (2.5 mg to 15 mg) in a standardised volume. The exact ml volume is determined by the manufacturer and remains consistent across all dose strengths. Your prescriber will specify which dose is appropriate for you.
Is Mounjaro injected into muscle or under the skin?
Mounjaro is injected subcutaneously (under the skin), not into muscle. Common injection sites include the stomach, upper thigh, or upper arm. Rotate injection sites each week to reduce skin irritation.
How does Mounjaro's dual mechanism differ from Wegovy?
Mounjaro activates both GIP and GLP-1 pathways; Wegovy activates GLP-1 only. This dual action in Mounjaro may contribute to appetite regulation and food cravings reduction, though both showed similar average weight loss in clinical trials.
Can you switch from Wegovy to Mounjaro partway through treatment?
Any change between medications must be managed by your prescriber. There is no official dose conversion chart, though approximate equivalences exist based on clinical practice. Your prescriber will advise on timing and any overlap needed.
What's the UK prescribing pathway for Mounjaro?
Mounjaro is prescription-only. NHS access is through specialist tier 3 weight management services (availability varies by region). Private access is available through online consultations with UK-licensed prescribers, followed by dispensing from a GPhC-registered pharmacy.
Ready to take control of your weight loss journey?
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