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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Mounjaro, Wegovy, and Hypoglycaemia — What's the Difference?
Hypoglycaemia (low blood sugar) is a rare side effect with both Mounjaro and Wegovy when used for weight management in non-diabetic adults. However, the two medications work through different mechanisms — Mounjaro is a dual GIP and GLP-1 receptor agonist, while Wegovy is a GLP-1 agonist only. Understanding how each medication affects glucose levels, and which is more suitable for your individual health profile, requires a clinical assessment from your GP or a licensed prescriber.
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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.
Clinical Trial Data and Glucose Effects
Both medications are licensed for weight management in UK adults and were studied in large clinical trials. The SURMOUNT trial (Mounjaro) and STEP trials (Wegovy) tracked glucose levels and hypoglycaemic events across thousands of participants.
In non-diabetic adults taking these medications for weight loss, hypoglycaemia is uncommon — reported in less than 2% of participants in most trials. However, the risk increases significantly in adults also taking diabetes medications like insulin or sulphonylureas. The dual GIP and GLP-1 mechanism of Mounjaro (tirzepatide) may theoretically offer more glucose regulation than the single GLP-1 pathway of Wegovy (semaglutide), though clinical superiority in glucose control has not been formally established. Your prescriber will assess your individual risk based on your medical history, current medications, and glucose control.
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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.
Who Is at Higher Risk and When to Seek Help
Hypoglycaemia risk is highest in adults taking these medications alongside diabetes medications — particularly insulin or sulphonylureas. If you are diabetic and prescribed Mounjaro or Wegovy, your diabetes medication doses will typically need adjustment. Non-diabetic adults rarely experience low blood sugar on these medications alone.
Symptoms of hypoglycaemia include shakiness, sweating, rapid heartbeat, confusion, and dizziness. If you experience these symptoms, eat or drink something with sugar immediately and contact your GP or call NHS 111. Always inform your prescriber of all medications you are taking — they will assess your personal hypoglycaemia risk and monitor you appropriately during 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.
Can Mounjaro cause hypoglycaemia in non-diabetic adults?
Hypoglycaemia is very rare in non-diabetic adults using Mounjaro for weight management alone. Clinical trials showed rates below 2%. Risk increases only if you are also taking diabetes medications like insulin or sulphonylureas — your prescriber will adjust these doses accordingly.
Is Wegovy safer than Mounjaro for glucose control?
Both medications are similarly safe for glucose control in non-diabetic adults. Wegovy uses a single GLP-1 pathway; Mounjaro uses dual GIP and GLP-1. Neither is inherently safer — suitability depends on your individual health profile, which your prescriber will assess.
What's the difference between Mounjaro's tirzepatide and Wegovy's semaglutide mechanism?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, activating two glucose-regulating pathways. Wegovy (semaglutide) is a GLP-1 agonist only. The dual mechanism may offer slightly more glucose regulation, but both are effective for weight management when used appropriately.
Should I stop my diabetes medication when starting Mounjaro or Wegovy?
No — do not stop diabetes medication without medical guidance. Your GP or prescriber will assess whether dose reductions are needed based on your glucose levels during treatment. Never adjust diabetes medication independently.
How is hypoglycaemia risk assessed before prescription?
Your prescriber will review your complete medical history, current medications, and glucose control. Use our free BMI calculator to understand your weight context, and bring all medication details to your appointment. Risk assessment is individualised — not everyone is equally at risk.
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.