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
What Does Mounjaro Do To Blood Sugar?
Mounjaro (tirzepatide) affects blood sugar by activating two natural hormone pathways — GIP and GLP-1 — that work together to help regulate glucose levels. Unlike insulin, Mounjaro doesn't directly lower blood sugar in healthy individuals, but it enhances your body's natural ability to manage blood glucose in response to food. This dual mechanism is what distinguishes it from other weight management injections like Wegovy, which uses GLP-1 alone. Understanding how Mounjaro works can help you and your GP decide if this prescription-only medicine is right for your individual health needs.
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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 Controls Blood Sugar Levels
Mounjaro's dual GIP and GLP-1 action mimics hormones your gut naturally produces after eating. When you consume food, these hormones signal your pancreas to release insulin proportionally — only when blood sugar actually rises. This means Mounjaro helps your body respond appropriately to meals without causing dangerously low blood sugar (hypoglycaemia) in people without diabetes.
The medication also slows gastric emptying — the rate at which food leaves your stomach — which reduces post-meal blood sugar spikes. Additionally, Mounjaro reduces glucagon secretion, a hormone that would otherwise raise blood sugar between meals. For adults with type 2 diabetes or prediabetes, this multi-action approach can significantly improve glucose control. Clinical data shows tirzepatide users experience meaningful improvements in HbA1c (a measure of average blood sugar over three months), though results vary individually. Your GP or specialist will monitor your blood sugar response during treatment.
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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.
Blood Sugar Effects: NHS Context and Safety
The NHS recognises Mounjaro as an effective option for eligible adults through tier 3 specialist weight management services. When prescribed for weight management in people without diabetes, Mounjaro's blood sugar benefits are a secondary effect — the primary goal is sustainable weight loss. If you have type 2 diabetes or prediabetes, your healthcare team will assess whether Mounjaro is appropriate and monitor your HbA1c and fasting glucose regularly.
Important safety consideration: If you're already taking diabetes medications such as insulin or sulphonylureas, your prescriber may need to adjust those doses to prevent hypoglycaemia. This is why Mounjaro is always prescribed following a thorough clinical assessment and requires ongoing GP monitoring. Use our free GLP-1 weight loss calculator to understand projected outcomes, and discuss blood sugar monitoring with your healthcare provider before starting treatment.
- 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.
Does Mounjaro work like insulin?
No. Mounjaro doesn't replace or mimic insulin directly. Instead, it enhances your body's natural ability to produce and release insulin in response to meals. It works through GIP and GLP-1 hormone pathways, not through insulin injection. This makes it fundamentally different from insulin therapy.
Can Mounjaro cause low blood sugar on its own?
In people without diabetes, Mounjaro alone is unlikely to cause dangerously low blood sugar because it only stimulates insulin release when blood glucose actually rises. However, if you're also taking diabetes medications like insulin or sulphonylureas, the combination could cause hypoglycaemia — which is why dose adjustments are often needed.
What's the difference between Mounjaro and Wegovy for blood sugar control?
Mounjaro uses dual GIP and GLP-1 activation, while Wegovy uses GLP-1 alone. Both help regulate blood sugar, but Mounjaro's dual mechanism may provide enhanced glucose control. Clinical trials show slightly better HbA1c improvements with tirzepatide, though individual results vary. Your GP can advise which is more suitable for you.
How often will my blood sugar be monitored on Mounjaro?
Your prescriber will typically check your blood sugar (fasting glucose and/or HbA1c) before starting Mounjaro, and then regularly during treatment — usually at least every 3–6 months initially. More frequent monitoring may be needed if you have diabetes or are taking other blood sugar medications. Your GP will advise your specific monitoring schedule.
Is Mounjaro prescribed on the NHS for blood sugar control?
Mounjaro is NICE-approved and available through NHS tier 3 specialist weight management services. Primary eligibility is based on BMI and weight-related health conditions — not diabetes alone. If you have type 2 diabetes with obesity, you may be eligible. However, availability varies significantly by region and waiting lists can be lengthy. Your GP can discuss NHS options with you.
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.