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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Is Mounjaro Insulin? Understanding the Difference
Mounjaro is not insulin, though the common confusion is understandable. Mounjaro (tirzepatide) is a prescription-only injection that works differently from insulin—it activates two natural hormone pathways (GLP-1 and GIP receptors) to help regulate appetite and support weight management. This guide explains how Mounjaro differs from insulin, who may be eligible for it in the UK under NHS guidance, and how to access it through either NHS specialist services or private prescribing.
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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 Differently from Insulin
Mounjaro is not insulin and does not work like insulin. Insulin is a hormone that directly regulates blood sugar by helping glucose enter cells. Mounjaro is a dual GLP-1 and GIP receptor agonist—it mimics and amplifies two natural gut hormones that signal fullness, reduce cravings, and slow gastric emptying.
- Insulin: Works by directly lowering blood glucose levels; used for diabetes management; requires careful monitoring; causes blood sugar to drop
- Mounjaro: Activates appetite-regulating pathways; approved for weight management; slows how quickly food leaves your stomach; does not directly lower blood sugar in non-diabetic individuals
Some patients with type 2 diabetes take both—Mounjaro for weight management and insulin for blood sugar control—but they are separate medicines with different mechanisms. Your prescriber will assess whether Mounjaro is suitable for you based on your individual health profile, including any diabetes diagnosis.
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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.
NHS Eligibility and UK Access Routes for Mounjaro
In the UK, Mounjaro is available through both NHS specialist services and private prescribing. NHS access: Requires referral from your GP to a tier 3 or tier 4 weight management service. NICE has approved tirzepatide (Mounjaro) for NHS use, though availability varies significantly by region and waiting times can be lengthy. Private access: Available through GPhC-registered online pharmacies following a clinical assessment with a UK-licensed prescriber—no NHS referral needed. Eligibility criteria are the same: BMI of 30 or above, or 27+ with weight-related health conditions such as type 2 diabetes, prediabetes, or high blood pressure. Use our free BMI calculator to check where you stand, and our GLP-1 weight loss calculator to explore potential outcomes with tirzepatide.
- 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 safe if I take insulin for diabetes?
Mounjaro and insulin work through different mechanisms and can be prescribed together if clinically appropriate. However, this requires careful monitoring by your healthcare team, especially if you take insulin—there is a small risk of low blood sugar. Always inform your prescriber about any diabetes medications you are taking.
Will Mounjaro lower my blood sugar like insulin does?
Mounjaro does not directly lower blood sugar in the way insulin does. It may modestly improve blood sugar control by slowing stomach emptying and reducing food intake, but it is not a replacement for insulin or other diabetes medications. It is approved for weight management, not diabetes treatment.
How is Mounjaro dosed compared to insulin?
Mounjaro is a once-weekly injection starting at 2.5 mg, increasing every 4 weeks up to a maximum of 15 mg. Insulin dosing is highly individualised and adjusted based on blood sugar readings. They are dosed differently because they have different purposes and mechanisms.
Can I get Mounjaro on the NHS if I take insulin?
Yes, you may be eligible for NHS Mounjaro if you meet BMI and health condition criteria, even if you take insulin. However, your prescriber will need to manage both medications carefully. NHS access requires referral to a specialist weight management service, which varies by region.
What's the difference between Mounjaro and Wegovy in terms of how they work?
Both are injectable weight management medications, but Mounjaro is a dual GIP and GLP-1 agonist, while Wegovy (semaglutide) activates only the GLP-1 pathway. This may mean Mounjaro offers slightly greater appetite suppression, though individual results vary significantly.
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.