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 Eye Side Effects — What You Need to Know
Mounjaro (tirzepatide) is a prescription-only weight management injection licensed in the UK. While nausea and stomach side effects are commonly reported, some users experience vision-related changes. This guide explains what eye side effects may occur with Mounjaro, who is at higher risk, and what NHS guidance recommends for monitoring. If you're considering Mounjaro or already taking it, understanding potential vision changes helps you recognise when to contact your GP. Use our free BMI calculator above to check your current health baseline before discussing treatment options with your prescriber.
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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.
Eye Side Effects Associated with Mounjaro
Eye and vision side effects are not listed as common side effects of Mounjaro in clinical trials, but some users report vision changes. The most important concern is diabetic retinopathy — a complication of diabetes affecting the blood vessels in the eye. Mounjaro can improve blood sugar control rapidly, and sudden improvements in glucose levels may temporarily worsen existing diabetic retinopathy symptoms before improving long-term.
Reported vision-related experiences include:
- Blurred vision or difficulty focusing
- Floaters (small spots or lines in your vision)
- Temporary vision changes as your body adjusts to the medication
- Worsening of existing diabetic eye disease (in people with type 2 diabetes)
Important: Mounjaro does not cause eye disease, but rapid blood sugar improvements may affect existing eye conditions. If you have diabetes and are considering Mounjaro, your prescriber must assess this risk during your clinical assessment.
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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.
NHS Monitoring and When to Seek Medical Attention
The NHS recommends that anyone starting Mounjaro should have baseline eye health information documented, especially if they have diabetes or diabetic retinopathy. Regular eye checks through your GP or optician are important throughout Mounjaro treatment. Contact your GP immediately if you experience: sudden vision loss, severe blurred vision, flashing lights, new floaters, or pain in the eye. These symptoms require urgent assessment to rule out serious complications like retinal detachment or diabetic emergencies. Your prescriber can discuss your individual risk and whether Mounjaro is suitable for you during your clinical assessment.
- 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 permanent eye damage?
Mounjaro itself does not cause eye disease, but rapid improvements in blood sugar levels may temporarily affect existing diabetic retinopathy. Long-term, better blood sugar control typically benefits eye health. Anyone with diabetes should have regular eye checks and inform their prescriber before starting Mounjaro.
Should I have an eye test before starting Mounjaro?
If you have type 2 diabetes or diabetic retinopathy, your prescriber will assess your eye health risk during your clinical assessment. A baseline eye test through your optician or eye clinic is sensible before starting, especially if you haven't had one recently.
What vision changes are considered normal with Mounjaro?
Minor blurred vision or slight focusing difficulty can occur as your body adjusts, particularly during dose increases. These typically resolve within days to weeks. Persistent or sudden vision changes are not normal and require GP assessment.
How do I report eye side effects to the NHS?
Contact your GP or prescriber immediately if you experience vision changes. You can also report suspected side effects to the MHRA's Yellow Card scheme online (yellowcard.mhra.gov.uk) or via your pharmacy.
Is Mounjaro safe for people with existing eye disease?
Mounjaro can be used safely in people with eye disease, but requires careful prescriber assessment beforehand. Rapid blood sugar improvements may initially affect vision, but long-term outcomes are typically positive. Your prescriber will discuss individual risk during consultation.
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.