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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What Is Mounjaro's Active Ingredient and How Much Does It Cost in the UK?
Mounjaro's active ingredient is tirzepatide, a dual GIP and GLP-1 receptor agonist that helps regulate appetite and blood sugar control. If you're considering this prescription weight management injection, understanding what it contains and what it costs in the UK is essential. This guide covers the ingredient, how it works, UK pricing, and how to access Mounjaro through NHS or private routes. Use our free GLP-1 weight loss calculator above to explore potential outcomes at different doses.
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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.
Understanding Tirzepatide: How Mounjaro's Active Ingredient Works
Tirzepatide is the active pharmaceutical ingredient in Mounjaro. It's a synthetic peptide that works as a dual receptor agonist—meaning it activates two hormone pathways in the body: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1). This dual mechanism is what distinguishes Mounjaro from other weight management injections like Wegovy, which targets GLP-1 only.
When you inject Mounjaro, tirzepatide mimics these natural hormones to help reduce appetite, increase feelings of fullness, and support better blood sugar control. It also slows gastric emptying—how quickly food moves through your stomach—though this effect typically reduces over time. The ingredient is supplied in a pre-filled KwikPen device as a sterile solution, available in doses ranging from 2.5 mg to 15 mg once weekly.
- Tirzepatide is made by Eli Lilly and Company
- Subject to additional MHRA monitoring (Black Triangle ▼ status)
- Each KwikPen contains 4 doses (4 weeks' supply)
- Stored in a refrigerator at 2–8°C before use
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.
Mounjaro Cost in the UK: NHS vs Private Access
NHS access: Mounjaro is available through NHS specialist tier 3/4 weight management services, but availability varies significantly by region and waiting lists can be lengthy. If your GP refers you to a specialist service and tirzepatide is approved, it's typically provided at no cost to you on the NHS.
Private prescription cost: Through private online prescribing with a UK-licensed prescriber, Mounjaro costs roughly £129–£320 per month depending on your dose. Prices vary between registered pharmacies. An initial online consultation usually costs £30–£60 and includes a clinical assessment to confirm you're eligible. Subsequent repeat prescriptions are often cheaper. Monthly costs increase with each dose escalation: the starting 2.5 mg dose is less expensive than the maximum 15 mg maintenance dose.
To access Mounjaro privately, you'll complete an online health questionnaire, consult with a UK-licensed prescriber (usually within 24–48 hours), and receive a prescription if deemed appropriate. The medication is then dispatched by a GPhC-registered pharmacy, typically arriving within 3–5 working days. You can calculate your potential weight loss outcomes using our free GLP-1 weight loss calculator above—this helps you understand realistic results at your chosen dose before committing to treatment.
- 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 Mounjaro?
Yes. Tirzepatide is the active pharmaceutical ingredient; Mounjaro is the brand name under which it's marketed in the UK by Eli Lilly. When your prescriber mentions tirzepatide, they're referring to the same medication as Mounjaro. Always check your prescription to confirm the exact medication and dose.
How does tirzepatide differ from semaglutide in Wegovy?
Tirzepatide (Mounjaro) activates both GIP and GLP-1 receptors, whilst semaglutide (Wegovy) activates GLP-1 only. This dual mechanism in Mounjaro may offer different weight loss outcomes. Clinical trials showed tirzepatide users lost approximately 15–21% body weight on average, compared to roughly 15% with Wegovy. Individual results vary significantly.
What is tirzepatide made from?
Tirzepatide is a synthetic peptide manufactured through recombinant DNA technology by Eli Lilly. It's a man-made protein that mimics natural hormones (GIP and GLP-1) produced in the body. Each KwikPen contains tirzepatide solution with inactive ingredients including sodium chloride, sodium phosphate dibasic, sodium phosphate monobasic, and water for injection.
Can I get Mounjaro free on the NHS in the UK?
Yes, through NHS specialist weight management services following a GP referral and clinical assessment. However, NHS availability varies by region and waiting lists can be very long (often months to years). Private prescription is faster but costs £129–£320 monthly. Ask your GP about specialist referral options in your area.
How quickly will I see results from tirzepatide?
Most people notice reduced appetite within the first 2–4 weeks. Measurable weight loss typically begins in weeks 4–8 as your body adjusts to the dose. Maximum results are usually achieved after 12–16 weeks on a stable dose. Use our free progress tracker to log your weekly weight and monitor your individual results over time.
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.