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
Does Mounjaro Cause Blindness? What UK Patients Should Know
Mounjaro (tirzepatide) does not directly cause blindness. However, there is a specific eye health concern relevant to people with type 2 diabetes or prediabetes: gradual weight management or significant changes in blood sugar control can potentially worsen existing diabetic retinopathy (damage to blood vessels in the eye). This is not unique to Mounjaro — it can occur with any gradual weight management or blood sugar changes. Understanding this risk and having regular eye checks with your GP or optician is important if you take this prescription medication.
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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.
Mounjaro, Diabetic Retinopathy, and Eye Safety in the UK
Diabetic retinopathy is damage to the blood vessels of the retina caused by high blood sugar over time. People with type 2 diabetes or prediabetes are at risk. The concern with Mounjaro is not that the medication itself damages eyes, but that rapid changes in blood sugar control can sometimes worsen existing diabetic retinopathy temporarily.
This risk is outlined in the MHRA product information and applies to all GLP-1 medications (including Wegovy) and gradual weight management methods generally. It is not specific to tirzepatide. The risk is most relevant for people who already have diabetic retinopathy.
- If you have type 2 diabetes with existing eye damage, inform your GP before starting Mounjaro
- Regular eye checks are essential — ideally every 12 months, or as recommended by your optician
- Report any vision changes (blurred vision, floaters, flashing lights) to your GP immediately
- Blood sugar management during weight loss should be monitored by your prescriber
Clinically BackedWeight Loss
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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 Safety and When to Seek Medical Advice
Mounjaro is a prescription-only medicine assessed for safety by the MHRA (Medicines and Healthcare products Regulatory Agency). It carries a Black Triangle (▼) status, meaning it is subject to additional monitoring — this is normal for newer weight management medicines.
Vision changes are not among the most common side effects reported in clinical trials. However, if you experience sudden blurred vision, eye pain, or changes in your sight after starting Mounjaro, contact your GP or optician immediately rather than waiting for a routine appointment. Calculate your BMI using our free BMI calculator to discuss your full health profile with your prescriber, especially if you have diabetes or prediabetes.
- 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 actually make you blind?
No. Mounjaro does not directly cause blindness. However, if you have existing diabetic retinopathy (eye damage from diabetes), rapid blood sugar changes associated with weight loss may temporarily worsen it. This is why regular eye checks are important if you have diabetes and take any weight loss medication.
Who is at risk of eye problems with Mounjaro?
People with type 2 diabetes or prediabetes who already have diabetic retinopathy are at higher risk of eye complications. People without diabetes or without existing diabetic retinopathy have minimal eye-related risk. Your GP can assess your individual risk during a clinical consultation.
Is this risk different from Wegovy or other weight loss injections?
No. All GLP-1 medications (Mounjaro, Wegovy, Saxenda) carry the same diabetic retinopathy consideration because they all improve blood sugar control. The risk applies to any significant and gradual weight management method. Your prescriber will discuss this with you based on your health history.
What eye symptoms should I report to my GP?
Contact your GP immediately if you experience sudden blurred vision, eye pain, flashing lights, new floaters, or any other vision change after starting Mounjaro. These symptoms could indicate retinopathy worsening or another condition requiring urgent assessment.
How often should I have eye checks while taking Mounjaro?
If you have diabetes, the NHS recommends an annual diabetic eye screening. If you start Mounjaro, discuss your eye check schedule with your GP — they may recommend checks more or less frequently depending on your individual risk. Opticians can also refer you for diabetic screening if needed.
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.