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 Vision Loss vs Wegovy — What the Evidence Shows
Vision changes are a possible side effect of both Mounjaro (tirzepatide) and Wegovy (semaglutide), though they are not common. Both medications work via similar hormone pathways and carry comparable eye safety profiles. This guide compares the clinical evidence, explains when vision changes may occur, and clarifies what prescribers monitor. Both are prescription-only weekly weight loss injections available in the UK following clinical assessment.
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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.
Clinical Evidence — Vision Loss in Mounjaro vs Wegovy Trials
Mounjaro (SURMOUNT trials): Vision-related adverse events were reported in less than 1% of trial participants. Most reports were mild and temporary, typically described as blurred vision or temporary visual disturbances. Severe vision changes requiring intervention were rare. The SURMOUNT-1 trial, which evaluated the highest dose (15 mg weekly), did not identify vision loss as a major safety concern.
Wegovy (STEP trials): Similarly, vision changes occurred in a very small percentage of participants in STEP-1 and related trials. Blurred vision and eye-related symptoms were uncommon and mostly resolved during continued treatment or after dose adjustment.
- Both medications: vision issues represent less than 1% of reported side effects overall
- Most cases are mild and temporary, not permanent
- Severe vision loss requiring treatment discontinuation is rare in both
- Individual variation is significant — most users experience no vision changes at all
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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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Why Vision Changes Can Occur — Mechanism Comparison
Both Mounjaro and Wegovy can theoretically affect vision through two mechanisms: gradual weight management itself (which may temporarily affect eye pressure or blood vessel function) and the medications' effects on blood sugar regulation. Mounjaro is a dual GIP and GLP-1 receptor agonist, while Wegovy is a GLP-1 agonist only. However, this mechanistic difference does not appear to translate to meaningfully different vision safety profiles in clinical practice.
Patients with pre-existing eye conditions—particularly diabetic retinopathy—require closer ophthalmological monitoring, regardless of which medication is prescribed. Your prescriber will assess your eye health history during the clinical assessment before starting either medication.
- 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 vision loss a common side effect of Mounjaro?
No. Vision loss or blurred vision is uncommon with Mounjaro—reported in less than 1% of clinical trial participants. Most cases reported were mild and temporary. Serious vision problems requiring medication discontinuation were rare. Individual results vary significantly; most users experience no vision changes at all.
Does Wegovy cause more or fewer vision problems than Mounjaro?
Clinical trial data suggests vision issues occur at similar low rates with both medications (under 1%). No robust head-to-head trial directly compared vision safety between them. Both carry comparable eye safety profiles. Your prescriber will assess which is more suitable based on your individual health history, not primarily on vision risk alone.
What should I do if I notice blurred vision while taking Mounjaro or Wegovy?
Contact your prescriber or GP immediately. Most vision changes resolve independently or with dose adjustment. However, sudden vision loss, persistent blurring, or flashing lights require urgent assessment. Do not stop the medication without guidance. If symptoms are severe, seek emergency eye care (A&E) or contact an optometrist urgently.
Will a prescriber check my eyes before starting Mounjaro or Wegovy?
Your prescriber will take a full health history, including any eye conditions or vision problems. If you have diabetes, pre-existing retinopathy, or significant eye disease, this will be documented. You may be referred for baseline eye assessment, especially if you have diabetic retinopathy. Ongoing eye health monitoring is part of responsible prescribing.
Are vision changes permanent with these weight loss injections?
No. In clinical trials, vision changes associated with Mounjaro and Wegovy were typically temporary and resolved during continued use or after dose adjustment. Permanent vision loss is extremely rare. However, anyone experiencing persistent vision symptoms should be assessed by an eye specialist to rule out other causes unrelated to the medication.
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