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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Blurred Vision and Mounjaro — Important Safety Information
Blurred vision is a less common side effect that some people experience when taking Mounjaro (tirzepatide), a prescription-only weight management injection. If you develop blurred vision while on Mounjaro, it's important to understand whether this is a normal adjustment reaction or something requiring urgent medical attention. This guide explains what you need to know about blurred vision as a potential Mounjaro side effect, when to contact your GP, and how it relates to your overall health and diabetes management.
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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.
Why Blurred Vision May Occur With Mounjaro
Blurred vision is not listed as a very common side effect of Mounjaro in clinical trials, but it has been reported by some users. There are several reasons why blurred vision may develop:
- Blood sugar changes: If you have type 2 diabetes or prediabetes, rapid improvements in blood sugar control when starting Mounjaro can temporarily affect vision. This is because the lens of the eye contains fluid that responds to blood sugar levels.
- Dehydration: Mounjaro commonly causes nausea and diarrhoea, which can lead to dehydration. Dehydration may cause temporary blurred vision.
- Diabetic retinopathy complications: In people with existing diabetic eye disease, rapid blood sugar improvements can sometimes worsen vision temporarily before improving.
- Individual sensitivity: Some people may be more sensitive to the medication's effects on fluid balance or hormone regulation.
Always inform your prescriber immediately if you experience new or worsening blurred vision while taking this tirzepatide injection.
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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.
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When to Seek Medical Help
Contact your GP or prescriber without delay if you experience:
- Sudden onset of blurred vision that develops quickly over hours or days
- Vision changes accompanied by other symptoms such as severe headache, eye pain, or flashing lights
- Blurred vision that does not improve after a few days or worsens over time
- Vision loss in one or both eyes
- Difficulty reading or driving safely due to vision problems
These symptoms could indicate a more serious condition such as diabetic retinopathy complications, increased eye pressure, or an unrelated eye condition requiring urgent attention. Your GP can refer you to an eye specialist if needed. Do not drive if your vision is significantly affected. While taking Mounjaro, attend regular eye checks as part of your routine healthcare — particularly important if you have diabetes.
- 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.
Is blurred vision a common side effect of Mounjaro?
Blurred vision is not listed as a very common side effect in clinical trials. More common side effects include nausea, diarrhoea, and constipation. However, blurred vision has been reported by some users, particularly those with existing diabetes. If you experience blurred vision, contact your prescriber for advice.
Could blurred vision be caused by improved blood sugar control?
Yes. In people with diabetes, rapid improvements in blood sugar levels when starting Mounjaro can temporarily affect vision because the eye lens responds to blood glucose changes. This effect is usually temporary, but you should still inform your GP if it occurs.
What should I do if I develop blurred vision while taking Mounjaro?
Contact your GP or prescriber immediately, especially if the blurred vision is sudden, severe, or accompanied by other symptoms. Do not drive if your vision is significantly impaired. Your GP may refer you to an eye specialist to rule out serious conditions such as diabetic retinopathy complications.
Can dehydration from Mounjaro cause blurred vision?
Yes. Mounjaro commonly causes nausea, vomiting, and diarrhoea, which can lead to dehydration. Dehydration may cause temporary blurred vision. Ensure you drink adequate fluids and contact your GP if vision problems persist despite staying well hydrated.
Should I stop taking Mounjaro if I experience blurred vision?
Do not stop taking Mounjaro without speaking to your prescriber first. However, contact them urgently if you develop blurred vision. They can assess whether the blurred vision is a temporary adjustment effect, medication-related, or something requiring further investigation — and advise whether continuing is safe.
Ready to take control of your weight loss journey?
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