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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Blurry Vision with Mounjaro — How It Compares to Wegovy
Blurry vision is not listed as a common side effect of Mounjaro (tirzepatide) in UK clinical trials, though visual changes can occasionally occur with GLP-1 and dual GIP/GLP-1 medications. If you're considering Mounjaro or comparing it to Wegovy (semaglutide), understanding potential side effects — and how they compare between the two medications — is important for making an informed choice with your prescriber. Both are prescription-only weight management injections licensed in the UK, but they work slightly differently and may affect individuals in different ways. Use our free BMI calculator to check your current health status, and our GLP-1 weight loss calculator to explore how each medication might support your journey.
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Calculate Your BMI Instantly
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.
How Mounjaro and Wegovy Differ in Mechanism and Trial Data
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — meaning it activates two natural hormone pathways to regulate appetite and blood sugar. Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating a single pathway. This difference in mechanism may influence how each medication affects individuals, though clinical trial data shows both support meaningful weight loss. In the SURMOUNT-1 trial, Mounjaro at 15 mg achieved approximately 20.9% average body weight loss over 72 weeks. In the STEP-1 trial, Wegovy at 2.4 mg achieved approximately 14.9% average weight loss over 68 weeks. Importantly, visual disturbances or blurry vision were not reported as common adverse effects in either trial. Vision changes may occur in individuals with existing eye conditions or rapid changes in blood sugar control, particularly in those with type 2 diabetes. Any concerning visual symptoms should be reported to your GP immediately.
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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.
Which Medication Is Right for You — Clinical Assessment Matters
Neither Mounjaro nor Wegovy is objectively "better" — suitability depends entirely on your individual health profile, medical history, and how your body responds. A UK-licensed prescriber will assess factors including your BMI, weight-related health conditions, current medications, any eye-related conditions, and contraindications before recommending either option. Both require a clinical assessment and prescription. Both are prescription-only medicines. If you have any pre-existing eye conditions — such as diabetic retinopathy, glaucoma, or macular oedema — inform your prescriber, as rapid changes in blood sugar control (which can occur with these medications) may temporarily affect vision. Your prescriber will weigh the benefits against any personal risk factors and determine which is most appropriate for you.
- 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 blurry vision?
Blurry vision is not listed as a common side effect in SURMOUNT clinical trials. However, visual changes can occasionally occur with GLP-1 and GIP/GLP-1 medications, particularly if you have existing eye conditions or experience rapid blood sugar changes. If you develop new visual symptoms, contact your GP immediately.
Is blurry vision more common with Mounjaro or Wegovy?
Neither medication lists blurry vision as a common adverse effect in clinical trials. Both may rarely cause temporary vision changes if blood sugar control changes rapidly. Prescriber guidance and individual health factors determine which is more suitable for you.
What should I do if I experience blurry vision while on Mounjaro?
Contact your GP or eye care professional immediately. Do not stop the medication without guidance. Your prescriber will assess whether the symptom is related to the medication, your blood sugar control, or an underlying eye condition requiring separate attention.
Are there other vision-related side effects to know about with these medications?
Changes in vision or diabetic retinopathy complications are possible if you have type 2 diabetes and experience rapid blood sugar changes. Inform your prescriber of any pre-existing eye conditions before starting either medication. Regular eye checks are recommended if you have diabetes.
How can I decide between Mounjaro and Wegovy?
Your prescriber will assess your individual health profile, BMI, weight-related conditions, medication interactions, and any pre-existing health conditions — including eye health. Both require a clinical assessment and prescription in the UK. Use our BMI calculator to understand your current health status and discuss options with your GP or licensed prescriber.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.