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. However, if you have type 2 diabetes or prediabetes, gradual weight management or changes in blood sugar control may temporarily affect vision. This is not blindness but a treatable condition. Understanding the vision risks and warning signs is important if you're considering this prescription-only injection. Always discuss any vision concerns with your GP before starting treatment.
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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.
Vision Changes and Mounjaro — What the Evidence Shows
Mounjaro itself does not cause blindness according to clinical trial data and post-marketing safety reports. However, vision changes can occur indirectly through two mechanisms:
- Rapid blood sugar changes: In people with diabetes, quick improvements in blood sugar control can temporarily blur vision as the lens of the eye adjusts to changing glucose levels. This usually resolves within weeks.
- Diabetic retinopathy: Existing diabetic retinopathy (damage to blood vessels in the retina from high blood sugar) may temporarily worsen when blood sugar control improves rapidly. This is not new blindness but a known complication in people with pre-existing eye disease.
The SURMOUNT clinical trials for Mounjaro (tirzepatide) did not report blindness as an adverse event. Vision changes were not listed as common or very common side effects. If you have diabetes or a history of eye problems, inform your prescriber before starting.
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.
Vision Warning Signs — When to Contact Your GP
Most people taking Mounjaro experience no vision problems. However, contact your GP immediately if you notice:
- Sudden blurred or cloudy vision
- Flashing lights or new floaters in your vision
- Dark spots or shadows in your visual field
- Difficulty reading or focusing on objects
- Eye pain or redness
These symptoms may indicate diabetic retinopathy progression, retinal detachment, or other eye conditions requiring urgent assessment—not blindness from Mounjaro itself, but conditions needing prompt evaluation. Your GP or an eye specialist can assess your vision quickly. Do not wait if symptoms develop suddenly.
- 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 damage the eyes or optic nerve?
No. Mounjaro (tirzepatide) does not directly damage the eyes, optic nerve, or retina. Clinical trials show no blindness or permanent vision damage caused by the medication itself. Vision changes, if they occur, are usually temporary and linked to blood sugar fluctuations in people with diabetes, not the drug directly.
Why do some people experience blurred vision on Mounjaro?
Blurred vision can occur when blood sugar levels change rapidly, which happens when Mounjaro improves glucose control. The lens of the eye changes shape in response to changing glucose levels, temporarily affecting focus. This effect typically resolves within a few weeks as the eye adjusts. It is not a sign of blindness.
Is Mounjaro safe if I have diabetic retinopathy?
If you have existing diabetic retinopathy, Mounjaro may be prescribed, but your prescriber needs to know. Rapid blood sugar improvement can temporarily worsen retinopathy in people with pre-existing eye disease. Regular eye checks with an optometrist or eye specialist are recommended. Your GP can help coordinate this monitoring.
Should I have an eye test before starting Mounjaro?
If you have diabetes, prediabetes, or any history of eye problems, inform your prescriber. An eye check before starting is not always necessary unless you have known diabetic retinopathy or other eye conditions. Your prescriber will assess whether monitoring is needed during treatment. Use our free GLP-1 weight loss calculator to explore your options alongside a full health assessment with your GP.
Is vision loss a common side effect of Mounjaro in the UK?
No. Vision loss or blindness is not a common or very common side effect of Mounjaro according to UK clinical data and the MHRA. The most common side effects are nausea, diarrhoea, and constipation. Temporary blurred vision from blood sugar changes is rare but possible in people with diabetes. Your GP can discuss your individual 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.