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 Are the Natural Ingredients in Mounjaro?
Mounjaro contains tirzepatide as its active ingredient — a synthetic compound that mimics natural hormones your body produces after eating. It's not derived from plants or natural sources, but designed to activate the same pathways. Understanding what's in your injection helps you discuss it confidently with your GP and identify any potential allergies or sensitivities before starting treatment.
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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 Ingredient and How It Works
Tirzepatide is the only active ingredient in Mounjaro. It's a dual GIP and GLP-1 receptor agonist — meaning it activates two natural hormone pathways your gut already uses. GLP-1 (glucagon-like peptide-1) and GIP (glucose-dependent insulinotropic polypeptide) are hormones your body produces naturally after meals to signal fullness and regulate blood sugar.
Tirzepatide is not extracted from plants or animals — it's a man-made compound created through synthetic chemistry. The Mounjaro KwikPen delivers a precisely measured dose of tirzepatide dissolved in a sterile solution. Unlike some diabetes medications, tirzepatide does not contain animal-derived insulin. This synthetic approach allows consistent dosing and purity, which is why it's prescription-only and requires specific storage (refrigerated until use).
- Dose range: 2.5 mg to 15 mg weekly
- Delivery: pre-filled auto-injection pen
- Mechanism: dual hormone pathway activation
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.
Excipients, Allergies, and Safety Considerations
Beyond tirzepatide, the Mounjaro solution contains excipients — inactive ingredients that stabilise the active compound and make injection possible. These include sodium phosphate dibasic dihydrate, sodium phosphate monobasic dihydrate, sodium chloride, and water for injection. Importantly, Mounjaro does not contain animal products, gluten, or latex in the needle guard.
If you're allergic to tirzepatide or any excipient, Mounjaro isn't suitable for you. Your GP or online prescriber will ask about allergies during assessment. Some people experience injection site reactions (redness, itching, bruising) — these are usually mild and temporary. Always inform your healthcare provider of all allergies before starting, and discuss any concerns about ingredients or dose titration during your initial consultation.
- 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 made from natural ingredients?
No. Mounjaro's active ingredient, tirzepatide, is a synthetic compound created through chemistry. It's not plant or animal-derived. However, it mimics natural hormones (GLP-1 and GIP) your body produces after eating. This synthetic approach ensures consistent dosing, purity, and safety — which is why it requires a prescription.
Can I take Mounjaro if I'm allergic to tirzepatide?
No. If you're allergic to tirzepatide or any ingredient in Mounjaro (including the excipients like sodium phosphate), the medication is not suitable for you. Always inform your GP or prescriber of all known allergies before assessment. They can discuss alternative weight loss options if Mounjaro isn't appropriate for your health profile.
Does Mounjaro contain animal products?
No. Mounjaro does not contain animal-derived ingredients. The active ingredient is synthetic, and the solution uses mineral salts and purified water. This makes it suitable for vegetarians and vegans. The needle guard contains no latex, but always check the full patient information leaflet if you have specific dietary or allergy concerns.
How does tirzepatide compare to Wegovy or natural weight loss methods?
Tirzepatide (Mounjaro) is a dual GIP+GLP-1 agonist, while Wegovy contains semaglutide (GLP-1 only). In clinical trials, Mounjaro showed slightly higher average weight loss (~21% body weight vs ~15% for Wegovy), though results vary individually. Natural methods like diet and exercise remain important alongside any medication.
What should I do if I experience an allergic reaction to Mounjaro?
Stop using Mounjaro immediately and seek urgent medical attention if you experience swelling of the face, lips, tongue, or throat, difficulty breathing, or severe rash. For milder reactions like injection site itching or mild rash, contact your GP. Always keep your prescriber informed of any side effects during dose titration to 15 mg.
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.