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
How Many mls in a Dose of Mounjaro?
Mounjaro (tirzepatide) comes in a pre-filled KwikPen device, and each pen contains four ready-to-use doses. The volume per injection varies depending on which dose strength you're prescribed, ranging from 0.5 ml for the lowest dose to 0.6 ml for the highest. Each pen is a once-weekly injection, and you'll rotate between injection sites. Understanding your dose volume is important for storage, injection technique, and knowing what to expect when using this prescription-only weight management 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 Dose Volumes and Strengths
Each Mounjaro dose is delivered in the following volumes:
- 2.5 mg dose: 0.5 ml per injection
- 5 mg dose: 0.5 ml per injection
- 7.5 mg dose: 0.5 ml per injection
- 10 mg dose: 0.5 ml per injection
- 12.5 mg dose: 0.5 ml per injection
- 15 mg dose: 0.6 ml per injection
The slight increase to 0.6 ml at the maximum 15 mg dose reflects the higher concentration of tirzepatide. All doses are delivered via the same KwikPen device, which is a pre-filled auto-injection pen. Each KwikPen contains exactly four doses (a four-week supply), meaning you'll use a new pen each month. The device has an easy-to-use dial mechanism for selecting your dose strength, and the injection takes just a few seconds. Storage matters: unopened pens must be kept refrigerated at 2–8°C, but after first use, pens can be kept at room temperature (below 30°C) for up to 30 days.
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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.
Getting Mounjaro on the NHS and Privately in the UK
Mounjaro is a prescription-only medicine in the UK and requires a clinical assessment before being prescribed. On the NHS, access is through specialist tier 3 or 4 weight management services — typically following a referral from your GP. Availability varies significantly by region and waiting times can be lengthy in many areas. Privately, you can obtain a prescription through a UK-licensed online prescriber following an online clinical consultation. Both routes require that you meet eligibility criteria: generally a BMI of 30 or above, or 27 or above with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. Your prescriber will assess whether Mounjaro is suitable for you based on your individual health profile. Use our free GLP-1 weight loss calculator to explore potential outcomes, and our BMI calculator to check where your current weight sits on NHS health thresholds.
- 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.
Is Mounjaro the same as Wegovy?
No. Both are prescription-only weight management injections available in the UK, but they work differently. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, while Wegovy (semaglutide) is a GLP-1 agonist only. Mounjaro's dual mechanism may explain why clinical trials showed slightly higher average weight loss (~20.9% at the maximum dose) compared to Wegovy (~15%). Both are once-weekly injections with similar side effects and require clinical assessment.
Can I switch from Mounjaro to another weight loss medication?
Yes, switching between weight management medications is possible and sometimes recommended based on individual response and side effects. Any switch must be managed by your prescriber — never stop one medication and start another without medical guidance. If considering a switch to Wegovy or another GLP-1 medication, discuss this with your GP or the prescriber managing your weight management. There is no official established conversion chart between Mounjaro and other medications, so your prescriber will determine the most appropriate equivalent dose.
How long do I need to stay on Mounjaro?
There is no set time limit for Mounjaro use. Treatment is typically ongoing as long as you continue to benefit from it and tolerate it well. Weight regain commonly occurs if treatment stops, so many people remain on the medication long-term. Your prescriber will review your progress regularly and discuss whether to continue, adjust the dose, or try a different approach. Some people use Mounjaro alongside lifestyle changes indefinitely, while others may eventually transition to maintenance with diet and exercise alone.
What happens if I miss a Mounjaro injection?
If you miss your weekly injection, the timing of your next dose depends on how late you are. If it's within 4 days of when you should have injected, take the missed dose as soon as you remember and continue your normal schedule from there. If it's more than 4 days since the scheduled injection, skip the missed dose and take your next dose on your normal weekly day. Never take a double dose to make up for a missed one. Maintain at least 72 hours (3 days) between injections.
Is Mounjaro available on the NHS for everyone who wants it?
No. NHS access to Mounjaro (tirzepatide) is through specialist weight management services, not standard GP prescription. You must meet eligibility criteria and typically need a GP referral to a tier 3 or 4 service. Regional variation is significant — some areas have well-resourced services with reasonable waiting times, while others have limited availability or lengthy queues. If NHS access is unavailable or the waiting time is too long, private prescription through an online licensed prescriber is an alternative, though this involves out-of-pocket costs.
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.