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 Mean? Understanding This Weight Loss Injection
Mounjaro is the brand name for tirzepatide, a prescription-only injection licensed in the UK for weight management in adults. The name itself is a brand identifier, but understanding what Mounjaro actually does—and how it differs from similar medications like Wegovy—helps you make informed decisions about weight management options available to you. This guide explains the meaning behind Mounjaro, how it works, and how it compares to other GLP-1 and GIP receptor agonist medications used 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.
How Mounjaro Works: Mechanism & Clinical Evidence
Mounjaro is a dual GIP and GLP-1 receptor agonist, which is what makes it unique among weight loss injections. It activates two natural hormone pathways in your body rather than one. GLP-1 (glucagon-like peptide-1) helps regulate appetite and blood sugar, while GIP (glucose-dependent insulinotropic polypeptide) supports fat utilisation and metabolic control. Together, these mechanisms may help reduce hunger, support feeling fuller after smaller meals, and assist with sustainable weight management.
- Clinical trial data (SURMOUNT-1): On average, adults taking Mounjaro at the maximum 15 mg dose lost approximately 20.9% of their body weight over 72 weeks, alongside reduced-calorie diet and increased physical activity.
- Dose range: Mounjaro is given as a once-weekly injection, starting at 2.5 mg and escalating to a maximum of 15 mg per week.
- Individual results vary significantly—clinical trial averages do not predict personal outcomes.
Calculate your potential weight loss at different doses using our GLP-1 weight loss calculator above.
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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.
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Mounjaro vs Wegovy: Key Differences & How to Choose
Wegovy (semaglutide) is a GLP-1 receptor agonist only—it works through a single hormone pathway rather than two. Wegovy reaches a maximum dose of 2.4 mg once weekly and showed average weight loss of approximately 14.9% body weight in clinical trials (STEP-1), also alongside lifestyle changes. Both Mounjaro and Wegovy are prescription-only UK medicines, but they differ in mechanism, dosing, and trial outcomes. Neither is inherently "better"—suitability depends on individual health factors, medical history, and prescriber assessment.
- Mounjaro: dual mechanism, higher trial weight loss averages, maximum 15 mg/week
- Wegovy: single mechanism, established long-term safety data, maximum 2.4 mg/week
- Both require clinical assessment before prescription—your GP or licensed prescriber will determine which is appropriate for you.
- 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.
What does "Mounjaro" actually mean as a brand name?
Mounjaro is the proprietary brand name for tirzepatide, a weight loss injection made by Eli Lilly. The name itself is a trademark identifier, but Mounjaro specifically refers to tirzepatide in its 2.5–15 mg doses licensed for weight management in adults.
Is Mounjaro the same as tirzepatide?
Yes, Mounjaro is the brand name for tirzepatide. When your GP or prescriber refers to "tirzepatide", they mean the same medication marketed as Mounjaro in the UK. Both terms are used interchangeably in clinical practice.
How is Mounjaro different from Wegovy in terms of how it works?
Mounjaro activates two hormone pathways (GIP and GLP-1), while Wegovy activates one (GLP-1 only). This dual mechanism in Mounjaro may support different metabolic effects, which is why clinical trial weight loss outcomes differed—Mounjaro showed approximately 20.9% average loss vs Wegovy's 14.9%.
Can I get Mounjaro on the NHS in the UK?
NICE has approved tirzepatide (Mounjaro) for use within NHS specialist weight management services. However, NHS access is through tier 3 specialist services following GP referral, availability varies significantly by region, and waiting lists can be lengthy. Private online prescribing is also available as an alternative.
Do I need a prescription for Mounjaro in the UK?
Yes, Mounjaro is prescription-only in the UK and requires clinical assessment by a licensed prescriber before being dispensed. You cannot purchase it without a valid prescription from a UK-licensed GP or prescriber, whether accessing it through the NHS or private channels.
Ready to take control of your weight loss journey?
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