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 and Retinopathy — What You Need to Know
If you have diabetic retinopathy or are considering Mounjaro (tirzepatide), it's important to understand the potential eye health implications. Mounjaro can cause changes in vision and may worsen existing diabetic retinopathy, particularly in people with type 2 diabetes. This UK health guide explains what retinopathy is, the risks associated with Mounjaro, and what the NHS recommends if you're thinking about this medication. Always discuss your eye health history with your GP or prescriber before starting any weight loss injection.
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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, Vision Changes, and Diabetic Retinopathy Risk
Diabetic retinopathy is damage to blood vessels in the retina caused by high blood sugar levels over time. It's a common complication of type 2 diabetes and can lead to vision problems or blindness if left untreated. Mounjaro works by improving blood sugar control, which is generally protective for eye health—however, rapid improvements in blood sugar can sometimes cause temporary vision changes or worsen existing retinopathy in the short term.
This effect is called acute diabetic retinopathy worsening and occurs because rapidly improving glucose control causes fluid shifts in the eye. In clinical trials, vision changes were reported as a side effect, and some participants with pre-existing diabetic retinopathy experienced deterioration. The risk is highest in people with:
- Poorly controlled type 2 diabetes before starting Mounjaro
- Existing diabetic retinopathy
- Rapid blood sugar improvement in the first weeks of treatment
The NHS and MHRA advise that anyone with diabetic retinopathy should have a comprehensive eye examination before starting Mounjaro and regular monitoring during treatment.
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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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What to Do If You Have Retinopathy: NHS Guidance
If you have diabetic retinopathy, inform your GP or prescriber immediately before starting Mounjaro. Your eye specialist and diabetes team need to coordinate your care. The NHS recommends:
- Eye examination before starting Mounjaro to establish a baseline
- Regular eye checks during treatment (frequency depends on retinopathy severity)
- Blood sugar monitoring to ensure gradual, sustainable control
- Immediate reporting of new vision changes, blurred vision, or floaters to your eye specialist
If you experience vision changes after starting Mounjaro—blurred vision, flashing lights, new floaters, or dark spots—contact your eye clinic or GP immediately. These could indicate retinopathy worsening and require urgent assessment. Mounjaro should be stopped if serious vision problems develop, pending eye specialist review.
- 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 I take Mounjaro if I have diabetic retinopathy?
You may be able to take Mounjaro with diabetic retinopathy, but it requires careful monitoring. Your GP, eye specialist, and diabetes team must coordinate your care, and you'll need baseline and regular eye examinations. The decision is based on the severity of your retinopathy, your overall health, and whether the benefits of improved blood sugar control outweigh the risks. Never start Mounjaro without disclosing existing eye problems to your prescriber.
Why can Mounjaro cause vision changes?
Mounjaro improves blood sugar control, which is good long-term for eye health. However, rapid improvements in glucose levels can cause fluid shifts in the eye and temporary vision changes. This is most likely in people with poorly controlled diabetes before treatment or existing retinopathy. Vision changes are usually temporary but require monitoring by an eye specialist.
What vision changes should I watch for when taking Mounjaro?
Report these symptoms to your eye clinic or GP immediately: blurred or cloudy vision, new floaters (spots drifting in your vision), flashing lights, dark spots or shadows, difficulty seeing at the edges of your vision, or eye pain. These could indicate worsening retinopathy and need urgent assessment. Don't wait for a routine appointment—seek same-day advice.
How often should I have eye checks while on Mounjaro?
Frequency depends on your baseline retinopathy status. People with no retinopathy should continue routine eye screening (typically every 1–2 years). Those with diabetic retinopathy need more frequent checks—typically every 3–6 months during Mounjaro treatment. Your eye specialist will set the schedule based on your individual risk. Your GP can refer you to the NHS Diabetic Eye Screening Programme if needed.
What's the difference between tirzepatide and other GLP-1 medications for eye safety?
Tirzepatide (Mounjaro) is a dual GIP/GLP-1 agonist, while Wegovy (semaglutide) is GLP-1 only. Both can cause vision changes if blood sugar control improves rapidly. The eye safety profile is broadly similar between GLP-1 medications—the risk depends more on how quickly your blood sugar falls than on which medication you use. Your prescriber and eye specialist will choose the safest option for your individual situation.
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