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
What's in Mounjaro? Complete Ingredient List
Mounjaro (tirzepatide) is a prescription-only weight management injection licensed in the UK. Understanding what's actually in your medication — the active ingredient and the other components that make up the KwikPen — helps you make informed decisions about your treatment. This guide explains the ingredient composition and what each component does.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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.
Active and Inactive Ingredients in Mounjaro
Active ingredient: Each Mounjaro KwikPen contains tirzepatide as the active component. Tirzepatide is a dual GIP and GLP-1 receptor agonist — it works by activating two natural hormone pathways in your body that help regulate appetite and blood sugar. The dose varies from 2.5 mg to 15 mg per weekly injection, depending on your individual treatment plan.
Inactive ingredients (excipients): The KwikPen also contains several inactive ingredients that help stabilise and preserve the medication:
- Sodium chloride (salt)
- Sodium phosphate dibasic heptahydrate
- Sodium dihydrogen phosphate dihydrate
- Disodium edetate dihydrate (EDTA)
- Water for injection
These excipients ensure the tirzepatide remains stable during storage and delivery. If you have allergies to any ingredient, discuss this with your prescriber before starting treatment.
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.
Why Ingredient Knowledge Matters for Your Treatment
Knowing the Mounjaro ingredient list is important if you have known allergies or sensitivities. Before starting a Mounjaro UK prescription, your prescriber will assess your medical history and medication allergies during the clinical assessment. Some people may experience injection site reactions (redness, bruising, or discomfort) — these are typically local responses to the injection itself rather than the tirzepatide ingredient. Understanding that Mounjaro is a dual-action medication (unlike Wegovy, which is a single GLP-1 agonist) helps explain why some users report different side effect profiles. Track any reactions using our free progress tracker to share with your healthcare provider at your next review.
- 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 tirzepatide the same as the medication in Wegovy?
No. Tirzepatide (Mounjaro) is a dual GIP and GLP-1 receptor agonist, while Wegovy contains semaglutide, which is a GLP-1-only agonist. Both are licensed for weight management in the UK, but they work via slightly different mechanisms. Clinical trials showed different average weight loss outcomes, though individual results vary.
Are there any common allergens in Mounjaro?
Mounjaro contains no common major allergens like peanuts, tree nuts, shellfish, or dairy. However, the formulation includes water, salts, and EDTA. If you have a known allergy to any ingredient listed, inform your prescriber before starting treatment. Most people tolerate the medication well.
Can I use Mounjaro if I'm allergic to sulphites or preservatives?
Mounjaro does not contain sulphites or common preservatives like methylparaben or propylparaben. The EDTA (ethylenediaminetetraacetic acid) is an established excipient used in many UK medicines. If you have specific concerns about any ingredient, discuss them with your GP or the prescriber conducting your clinical assessment.
Does Mounjaro contain lactose or gluten?
No, Mounjaro does not contain lactose or gluten. The injection is suitable for people with coeliac disease or lactose intolerance. However, always confirm this with your prescriber if you have severe allergies or intolerances, as formulations can occasionally change.
How long does Mounjaro stay in your system after injection?
Tirzepatide is absorbed gradually after injection and reaches peak levels around 1–3 days later. It has a half-life of approximately 5 days, meaning it takes about 5 days for half the dose to leave your system. You inject once weekly because the medication provides effect throughout the week. Most tirzepatide clears your system within about 2–3 weeks of your last dose.
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.