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
Mounjaro And Insulin — What's The Difference?
Mounjaro (tirzepatide) is often confused with insulin, but they are completely different medicines that work in different ways. Mounjaro is a prescription-only weight management injection licensed in the UK, whilst insulin is a hormone replacement therapy used primarily in diabetes care. Understanding the difference is important if you're considering prescription weight loss treatment or managing type 2 diabetes. This guide explains how they work, who uses them, and why they're not interchangeable.
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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 And Insulin Work Differently
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it mimics two natural hormones that regulate appetite and blood sugar. It sends signals to your brain to reduce hunger, helps you feel fuller after eating, and slows how quickly food leaves your stomach. Importantly, Mounjaro does not replace or mimic insulin itself.
Insulin, by contrast, is a hormone that manages blood glucose directly. When you eat, insulin helps cells absorb glucose from the bloodstream to use as energy. People with type 1 diabetes produce no insulin, so they must inject it. People with type 2 diabetes may eventually need insulin if their pancreas cannot produce enough.
- Mounjaro: works on appetite and weight regulation
- Insulin: works on blood glucose management
- Mounjaro is not insulin and does not replace insulin therapy
- Some people with type 2 diabetes use both — they serve different purposes
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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 And Insulin — Clinical Use And Eligibility
Mounjaro is prescribed for weight management in UK adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions. It requires a clinical assessment and prescription from a licensed prescriber. Insulin is prescribed by GPs or diabetes specialists for people who need blood glucose support — typically type 1 diabetes or advanced type 2 diabetes.
If you have type 2 diabetes and are considering Mounjaro, your prescriber will assess whether it's suitable alongside any insulin you may be taking. Some people benefit from both treatments, as they address different health needs. Use our free GLP-1 weight loss calculator above to explore potential outcomes, and discuss all options with your GP to determine the right approach for your individual health situation.
- 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 insulin?
No. Mounjaro (tirzepatide) is a GIP/GLP-1 receptor agonist that regulates appetite and weight. Insulin is a hormone that manages blood glucose levels. They work in completely different ways and serve different purposes in diabetes and weight management.
Can you take Mounjaro if you use insulin?
Yes, some people take both. If you use insulin for type 2 diabetes and are considering Mounjaro for weight management, your prescriber will assess whether they can be used together safely. Always inform your prescriber of all medications you take.
Does Mounjaro contain insulin?
No. Mounjaro does not contain insulin. It is a synthetic GIP/GLP-1 receptor agonist — a different type of injectable medicine designed to regulate appetite, not blood glucose directly.
Who needs insulin versus Mounjaro?
Insulin is needed by people with type 1 diabetes and some with advanced type 2 diabetes to manage blood glucose. Mounjaro is prescribed for weight management in adults with obesity or overweight with health conditions, regardless of diabetes status.
Does Mounjaro help with blood sugar like insulin does?
Mounjaro can support blood sugar control in type 2 diabetes because GLP-1 stimulates insulin release in response to food. However, it is not a direct blood glucose therapy like insulin — it works indirectly through appetite regulation and gut hormone pathways.
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.