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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Can Mounjaro Cause Eye or Vision Side Effects?
Mounjaro (tirzepatide) is a prescription-only weight management injection that may cause various side effects, including eye-related changes in some users. While vision problems are not listed as very common side effects, diabetic retinopathy complications and changes in vision have been reported. If you're considering Mounjaro or already using it, understanding potential eye effects is important for your safety. This guide explains what the evidence shows, who should be particularly cautious, and when to 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 the Clinical Evidence Shows About Mounjaro and Eyes
In the SURMOUNT clinical trials, Mounjaro was studied in thousands of adults over many weeks. Changes in vision were recorded as an uncommon side effect — not affecting everyone but documented in the safety data. The mechanism appears related to how tirzepatide affects blood sugar control and fluid balance in the body.
People with type 2 diabetes or a history of diabetic retinopathy face a higher risk because rapid blood sugar changes can trigger or worsen eye complications. This is why your prescriber will ask about your diabetes status before starting Mounjaro. If you're on Mounjaro and notice sudden vision changes, blurred vision, flashing lights, or new floaters, seek medical attention promptly — these can indicate diabetic retinopathy, which requires urgent assessment. Non-diabetic users report vision changes less frequently, but they can still occur.
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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.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
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Who Should Be Especially Cautious With Mounjaro and Eyes
If you have type 2 diabetes, especially if it's not well-controlled, your risk of vision-related side effects increases. You should have an eye health check before starting Mounjaro and inform your eye care professional that you're considering or using this medication. Those with a personal history of diabetic retinopathy or other eye conditions should discuss this with their prescriber before starting — Mounjaro may not be suitable, or additional monitoring may be needed.
Even without diabetes, any sudden vision changes while on Mounjaro warrant immediate GP contact. Your prescriber can adjust your dose, switch you to an alternative like Wegovy (which is a GLP-1 agonist with a single mechanism), or investigate whether another cause is responsible. Track any changes in your vision using a personal health diary or our free progress tracker.
If you have type 2 diabetes, especially if it's not well-controlled, your risk of vision-related side effects increases. You should have an eye health check before starting Mounjaro and inform your eye care professional that you're considering or using this medication. Those with a personal history of diabetic retinopathy or other eye conditions should discuss this with their prescriber before starting — Mounjaro may not be suitable, or additional monitoring may be needed.
Even without diabetes, any sudden vision changes while on Mounjaro warrant immediate GP contact. Your prescriber can adjust your dose, switch you to an alternative like Wegovy (which is a GLP-1 agonist with a single mechanism), or investigate whether another cause is responsible. Monitoring your health is easy with available tools — use our free BMI calculator and GLP-1 weight loss calculator to track your overall progress and discuss any concerns with your healthcare team.
- 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.
What vision changes are reported with Mounjaro?
Changes in vision, blurred vision, and complications of diabetic retinopathy have been documented in clinical trials and post-market reports. These are not very common but require prompt attention. Sudden vision changes, flashing lights, new floaters, or blurred vision warrant immediate GP contact to rule out serious eye conditions.
Is Mounjaro safe if I have diabetes?
Mounjaro can be prescribed to people with type 2 diabetes and is actually studied in this population. However, those with existing diabetic retinopathy or poorly controlled diabetes face higher risk of vision complications. Your prescriber will assess your individual suitability and may recommend eye screening before starting.
Can I use Mounjaro if I've had eye problems before?
If you have a history of eye disease, diabetic retinopathy, or vision problems, inform your prescriber before starting Mounjaro. They will assess whether Mounjaro is appropriate for you or whether an alternative weight management medication might be safer given your medical history.
How quickly do vision side effects appear?
Vision changes can occur at any point during Mounjaro treatment — early on or after several weeks. Most reported cases appear within the first few weeks of starting or after dose increases. Contact your GP if you notice any vision changes, regardless of how long you've been on Mounjaro.
What should I do if my vision changes while taking Mounjaro?
Stop taking Mounjaro and contact your GP immediately if you experience sudden vision changes, blurred vision, flashing lights, new floaters, or eye pain. Your prescriber may lower your dose, switch you to Wegovy or another medication, or investigate other causes. Never ignore vision changes — timely intervention is essential.
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