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
Can Mounjaro Cause Blindness?
Mounjaro (tirzepatide) does not directly cause blindness, but there is an important safety consideration for people with existing type 2 diabetes: the medication may affect diabetic retinopathy (eye damage caused by high blood sugar). If you have diabetes and are considering Mounjaro as a weight loss treatment, understanding this risk is essential. This guide explains what the evidence shows, who needs to be most cautious, and how to protect your eye health.
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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.
Mounjaro and Diabetic Retinopathy — What the Evidence Shows
Mounjaro itself does not cause blindness or directly damage the eyes. However, people with type 2 diabetes or prediabetes face a specific risk: rapid improvements in blood sugar control can temporarily worsen existing diabetic retinopathy (damage to the blood vessels in the retina caused by persistently high blood sugar).
This is not unique to Mounjaro — it can occur with any GLP-1 medication (including Wegovy, which contains semaglutide) or rapid diabetes treatment. When blood sugar drops quickly, the eyes can experience a temporary worsening of retinopathy before improvement occurs. This is called "early diabetic macular oedema" and is usually reversible, but it is a real safety consideration.
The SURMOUNT clinical trials that tested Mounjaro in weight management did not specifically report vision loss or blindness as a side effect. However, people with existing eye complications from diabetes must have their eyes monitored during treatment.
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.
Who Needs to Be Most Cautious and What to Do
If you have type 2 diabetes with existing retinopathy (eye damage), inform your prescriber before starting Mounjaro. You may need regular eye screening during the first few months of treatment, especially as your blood sugar improves. An ophthalmologist or optometrist can monitor for any temporary worsening.
If you have diabetes without retinopathy, or if you have prediabetes only, the risk is significantly lower. However, your GP or prescriber should still assess your individual eye health history. The NHS recommends eye screening for all people with diabetes regardless of weight loss medication.
Use our free GLP-1 weight loss calculator to estimate your potential weight and blood sugar improvements — rapid improvements are typically beneficial long-term, but medical monitoring during early treatment is sensible if you have existing eye complications.
If you develop any vision changes during Mounjaro treatment — blurred vision, floaters, loss of peripheral vision, or dark spots — seek urgent medical advice from your GP or eye care specialist. These symptoms require immediate evaluation, though they may not necessarily be related to Mounjaro.
Mounjaro improves blood sugar control by activating GLP-1 and GIP receptors, which support insulin release and reduce glucose levels. This metabolic improvement is generally protective for eye health long-term, but the transition period requires care if you have existing retinopathy.
- 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 cause blindness directly?
No. Mounjaro does not directly cause blindness or eye damage. However, if you have existing diabetic retinopathy (eye complications from high blood sugar), rapid blood sugar improvement during treatment may temporarily worsen your symptoms before improving them. This is called early diabetic macular oedema and is usually reversible.
Who is at risk of vision problems with Mounjaro?
People with type 2 diabetes who already have diabetic retinopathy (eye damage) are at highest risk of temporary vision changes. Those with diabetes without retinopathy, or those with prediabetes only, have lower risk. Anyone with a history of eye problems should inform their prescriber.
What should I do if I have diabetes and want to start Mounjaro?
Tell your prescriber about any existing eye conditions or diabetes complications. You may need eye screening before starting and during the first few months of treatment. Regular monitoring by an optometrist or ophthalmologist is recommended if you have retinopathy.
Is Mounjaro safer for vision than other weight loss injections?
All GLP-1 and GIP/GLP-1 medications (including Wegovy with semaglutide and Mounjaro with tirzepatide) carry the same retinopathy risk in people with existing eye damage. The risk relates to rapid blood sugar improvement, not to a specific medication.
What vision symptoms should prompt me to seek urgent help?
Contact your GP or eye care specialist immediately if you experience blurred vision, sudden vision loss, floaters, dark spots, or loss of peripheral vision during Mounjaro treatment. While these symptoms may not be related to the medication, they require urgent professional evaluation.
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.