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
Is Mounjaro Insulin?
Mounjaro is not insulin. It's a prescription-only injection called tirzepatide that works differently — it's a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways to help regulate appetite and support weight management. Available in the UK through NHS specialist services or private prescribing, Mounjaro comes in a pre-filled KwikPen device and is injected once weekly. Understanding how it works, how it differs from insulin, and whether you might be eligible can help you make informed health decisions with your GP.
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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.
How Mounjaro Works (It's Not Insulin)
Mounjaro contains tirzepatide, which mimics two natural gut hormones: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1). These hormones regulate appetite and how your body uses food — they're not insulin itself. Insulin controls blood sugar by moving glucose into cells; tirzepatide works on a different system entirely, signalling to your brain that you're full and supporting feeling satisfied after smaller meals. It also slows how quickly food leaves your stomach. This dual-hormone approach is what distinguishes Mounjaro from other weight management injections like Wegovy (semaglutide), which activates only GLP-1. Importantly, Mounjaro is not a diabetes medication, though it may help improve blood sugar control as a secondary benefit in some patients.
- GIP and GLP-1 are natural hormones, not insulin
- Mounjaro signals fullness and reduces food cravings
- Works on appetite regulation, not blood sugar directly
- Available via tirzepatide as a once-weekly injection
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 vs Insulin and Other Medications
If you take insulin for type 2 diabetes, Mounjaro works alongside it in a different way — your prescriber may adjust insulin doses if you use both. Insulin replaces or supplements the hormone your pancreas produces; Mounjaro doesn't replace insulin but supports appetite control and may improve overall metabolic health. The UK KwikPen delivery is straightforward: rotate injection sites (stomach, thigh, or upper arm) once weekly. Our GLP-1 weight loss calculator can help you estimate potential weight loss at different Mounjaro doses, though individual results vary. Always inform your GP of all medications, especially if you're using insulin, as dose adjustments may be needed during treatment 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 the same as insulin?
No. Mounjaro (tirzepatide) is a GIP and GLP-1 receptor agonist that works on appetite regulation. Insulin controls blood sugar directly. They're different medications with different mechanisms. Mounjaro is not insulin and does not replace insulin if you use it for diabetes.
Can I take Mounjaro if I use insulin?
Yes, but your prescriber must assess your individual situation. If you take insulin, your doses may need adjusting when starting Mounjaro, as your overall metabolic needs may change. Always inform your GP about all medications before beginning tirzepatide treatment.
How is Mounjaro prescribed in the UK?
Mounjaro is prescription-only. Access is through NHS tier 3 specialist weight management services (following GP referral) or private online prescribing. You'll require a clinical assessment to confirm eligibility based on your BMI and health conditions.
What's the starting dose of Mounjaro in the UK?
The starting dose is 2.5 mg once weekly, injected using a pre-filled KwikPen. Your prescriber increases the dose every 4 weeks, typically aiming for a maintenance dose. Maximum dose is 15 mg once weekly.
How quickly does Mounjaro work?
Most people notice appetite changes within the first 1–2 weeks, though weight loss develops gradually. In clinical trials (SURMOUNT-1), average weight loss over 72 weeks at the 15 mg dose was approximately 20.9% of body weight — results vary significantly between individuals.
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.