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 Does Mounjaro Contain?
Mounjaro contains tirzepatide, a dual GIP and GLP-1 receptor agonist that works differently from other weight loss injections. Available as a once-weekly injection in the UK, Mounjaro is a prescription-only medicine approved by the MHRA for weight management in adults. This guide explains the active ingredient, how it works, and what you need to know about Mounjaro on the NHS and through private prescribing in the UK.
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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.
The Active Ingredient: Tirzepatide
Tirzepatide is the active pharmaceutical ingredient in Mounjaro. Unlike older GLP-1 medications, tirzepatide is a dual receptor agonist — it activates both GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) pathways simultaneously.
This dual mechanism may explain why Mounjaro shows slightly higher average weight loss in clinical trials compared to single GLP-1 agents like Wegovy. In the SURMOUNT-1 trial, participants on the maximum 15 mg dose lost an average of approximately 20.9% of body weight over 72 weeks, though individual results vary significantly.
Tirzepatide helps regulate appetite, reduces food cravings, and supports feelings of fullness after smaller meals. It also slows gastric emptying — how quickly food leaves the stomach — though this effect typically decreases over time. The Mounjaro KwikPen delivers tirzepatide as a pre-filled injection administered once weekly into the stomach, thigh, or upper arm.
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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.
Mounjaro on the NHS and Private Access in the UK
In the UK, NICE has approved tirzepatide (Mounjaro) for use within specialist NHS weight management services for adults with a BMI of 30 or above, or 27 or above with weight-related health conditions like type 2 diabetes or cardiovascular disease.
Availability through the NHS varies significantly by region — many areas have long waiting lists for tier 3 specialist services. Private prescribing is available through UK-licensed prescribers following an online clinical assessment, without requiring NHS referral.
Your GP can discuss eligibility and whether Mounjaro is appropriate for you. Calculate your BMI and explore potential weight loss outcomes using our GLP-1 weight loss calculator to understand whether you might meet eligibility criteria.
- 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 contain different active ingredients. Mounjaro contains tirzepatide (a dual GIP+GLP-1 agonist), while Wegovy contains semaglutide (a GLP-1-only agonist). Mounjaro vs Wegovy shows tirzepatide may produce slightly higher average weight loss, but individual results vary. Both are prescription-only and require clinical assessment.
What excipients are in Mounjaro?
Besides tirzepatide, Mounjaro contains sodium chloride, sodium phosphate dibasic heptahydrate, sodium dihydrogen phosphate dihydrate, and water for injection. These inactive ingredients help stabilise and deliver the medication. The full list is available in the patient information leaflet (PIL) from your pharmacist or prescriber.
Can I be allergic to Mounjaro?
Yes. Some people may experience allergic reactions to tirzepatide or excipients in Mounjaro. Signs include swelling of the face, lips, tongue, or throat, severe rash, or difficulty breathing. If you have a known allergy to tirzepatide or any ingredients, inform your prescriber before treatment. Always disclose allergies during your clinical assessment.
How does Mounjaro's mechanism differ from older weight loss injections?
Mounjaro's dual GIP+GLP-1 action is unique among licensed UK weight loss medications. This combined mechanism may enhance appetite suppression and metabolic effects compared to single GLP-1 agents. However, side effects and dose titration schedules also differ — Mounjaro uses a slower titration than Wegovy, starting at 2.5 mg and increasing over 16+ weeks to the maximum 15 mg dose.
Is Mounjaro available on the NHS for everyone?
Not immediately. NHS access is through tier 3 specialist weight management services following referral from your GP. Eligibility requires BMI ≥30, or ≥27 with comorbidities. Availability and waiting times vary by region and ICB. Private prescribing offers faster access without NHS referral, though at personal cost.
Ready to take control of your weight loss journey?
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