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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Does Mounjaro Affect Eyesight?
Mounjaro (tirzepatide) is a prescription-only weight management injection licensed in the UK. If you're considering this medication, you may have questions about potential effects on eyesight. The short answer is that vision problems are not listed as a common side effect in clinical trials or UK guidance. However, some patients taking GLP-1 medications have reported changes in vision, particularly those with type 2 diabetes. This guide explains what the evidence shows and when you should contact your GP.
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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.
What Does the Evidence Show About Mounjaro and Vision?
Clinical trial data from Mounjaro does not identify vision changes or eye problems as a frequent side effect. The SURMOUNT-1 trial, which tested tirzepatide in adults with obesity, reported nausea, diarrhoea, vomiting, and constipation as the most common effects — but not eyesight issues. Vision problems are not listed in the standard side effects profile for Mounjaro in the UK Product Information guidance.
That said, GLP-1 medications including semaglutide (Wegovy) and tirzepatide (Mounjaro) have been associated with reports of blurred vision or temporary vision changes in some patients. These are typically mild and short-lived, but they are monitored. The mechanism is not fully understood, though rapid blood sugar changes in people with diabetes may play a role. If you develop blurred vision, sudden visual changes, or eye pain while taking Mounjaro, contact your GP or eye care specialist promptly.
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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.
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When to Contact Your GP About Vision Changes
Vision changes can occasionally signal a more serious condition, particularly if you have type 2 diabetes or are at risk of diabetic retinopathy (damage to the blood vessels in the retina). Contact your GP immediately if you experience:
- Sudden blurred or cloudy vision
- Flashing lights or new floaters in your vision
- Dark spots or loss of vision in part of your visual field
- Eye pain or discomfort
- Difficulty seeing at night
Your prescriber will assess whether Mounjaro remains appropriate for you. If you have existing eye conditions, inform your healthcare provider before starting Mounjaro, as they may recommend eye screening or closer monitoring.
- 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 vision loss?
There is no evidence in clinical trials that Mounjaro causes permanent vision loss. Vision changes reported with GLP-1 and GIP/GLP-1 medications are typically temporary. However, if you experience sudden or persistent vision changes, contact your GP or eye specialist immediately for assessment.
Is Mounjaro safe for people with diabetes-related eye problems?
If you have diabetic retinopathy or other eye complications from diabetes, you can still take Mounjaro — but your prescriber must know about it. They may recommend baseline eye screening and closer monitoring. GLP-1 medications can actually improve blood sugar control, which may benefit eye health long-term.
How does tirzepatide compare to Wegovy regarding eyesight?
Both tirzepatide (Mounjaro) and semaglutide (Wegovy) are GLP-1-based medications with similar side effect profiles. Vision problems are not common with either, but both are monitored for this. Individual responses vary — some people experience no vision changes on either medication.
Should I get an eye test before starting Mounjaro?
There is no standard requirement for an eye test before starting Mounjaro. However, if you have diabetes, existing eye conditions, or visual symptoms, inform your GP during your clinical assessment. They may recommend an eye check-up as part of your overall health review.
What should I do if my vision becomes blurry after my Mounjaro injection?
Blurred vision after an injection could be coincidental rather than medication-related. However, contact your GP to report it — do not drive or operate machinery until your vision is clear. Your prescriber can assess whether the timing relates to your injection and advise on next steps.
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