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 — Important Information
While nausea and digestive side effects are most common with Mounjaro (tirzepatide), some people report eye-related changes. Vision problems are not listed as a very common side effect, but they can occur and require attention. If you're considering Mounjaro or taking it as a weight management injection, understanding potential eye complications—particularly if you have type 2 diabetes or prediabetes—is important for your safety. This guide explains what eye side effects may occur, who is at higher risk, and when to contact your GP.
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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.
Eye-Related Side Effects and Vision Changes
Eye side effects with Mounjaro are not common, but they can happen. The main concern is diabetic retinopathy—damage to blood vessels in the retina of the eye. This risk is highest in people with type 2 diabetes, particularly if blood sugar control improves rapidly.
- Blurred vision or changes in focus
- Difficulty seeing clearly at distance or near
- Floaters (small spots drifting in vision)
- Eye pain or discomfort
- Sensitivity to light
These changes may be temporary, especially early in treatment. However, rapid improvements in blood sugar control—which Mounjaro can cause—may temporarily worsen diabetic retinopathy if present. This is why baseline eye checks are recommended before starting any tirzepatide therapy, particularly if you have diabetes. If you wear glasses or contact lenses, your prescription may also need adjustment.
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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.
When to Seek Medical Attention
Contact your GP immediately if you experience sudden vision loss, severe eye pain, or sudden onset of floaters or flashing lights. These can indicate serious eye conditions requiring urgent attention. Additionally, if you notice gradual changes in your vision—blurriness that doesn't improve with blinking, difficulty reading, or colour vision changes—report this to your GP within a few days. If you have type 2 diabetes or prediabetes, inform your eye care professional (optician or ophthalmologist) that you're taking Mounjaro before starting treatment. They may recommend more frequent eye checks during your first months on the medication. Our BMI calculator can help you understand your individual health risk profile, and your GP can assess whether Mounjaro is suitable for your specific circumstances.
- 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 directly cause permanent eye damage. However, if you have type 2 diabetes, rapid improvements in blood sugar control may temporarily worsen diabetic retinopathy. Baseline eye checks before treatment and regular monitoring help protect your vision. Most vision changes resolve once your body adjusts to the medication.
Is diabetic retinopathy a common side effect of Mounjaro?
Diabetic retinopathy is not listed as a common side effect. However, it is a known risk in people with existing diabetes when blood sugar control improves rapidly. This is why eye monitoring is recommended before and during tirzepatide treatment if you have diabetes.
Should I have an eye test before starting Mounjaro?
Yes. If you have type 2 diabetes or prediabetes, an eye check with an optician or ophthalmologist is strongly recommended before starting Mounjaro. This establishes a baseline and helps detect any existing retinopathy. Inform your eye care professional that you're starting tirzepatide.
Can Mounjaro change my glasses prescription?
Yes. Changes in blood sugar levels and fluid balance can temporarily affect the shape of the lens in your eye, potentially changing your glasses prescription. If you notice vision changes after starting Mounjaro, wait at least 4–6 weeks before updating your prescription, as changes often stabilise once your body adjusts.
What should I do if I notice blurred vision while taking Mounjaro?
Blurred vision may be temporary, especially in the first few weeks, but you should report it to your GP. They can determine whether it's a normal adjustment effect or requires further investigation. Do not ignore sudden or severe vision changes—contact your GP immediately or seek urgent care if vision loss is sudden.
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