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
Free tracker included with every download this week
Mounjaro and Blindness — What You Need to Know
There is no direct link between Mounjaro itself and blindness. However, the medication can cause diabetic retinopathy (eye problems) in people with existing type 2 diabetes, particularly if blood sugar control changes rapidly. This is why NHS prescribers carefully assess your health before offering this tirzepatide injection. If you have diabetes or are considering Mounjaro through the NHS or private prescription, understanding these risks is essential for your safety.
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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.
How Mounjaro Affects Vision and Blood Sugar Control
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist that improves blood sugar control in people with type 2 diabetes or prediabetes. When blood sugar levels change rapidly — such as when starting a new medication alongside weight loss — existing diabetic retinopathy (damage to the blood vessels in the eye) can temporarily worsen. This is not unique to Mounjaro; any medication that quickly lowers blood sugar can trigger this effect in people with uncontrolled diabetes.
The MHRA (UK medicines regulator) has identified this as a recognised risk, particularly in patients with pre-existing diabetic eye disease. This is why:
- Your prescriber will ask about your diabetes history and current eye health before issuing a prescription
- Patients with known diabetic retinopathy may need more frequent eye monitoring whilst taking Mounjaro
- Blood sugar control should be optimised gradually rather than rapidly
- Regular GP check-ups are essential during treatment
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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.
NHS Prescribing and Eye Health Screening
Before the NHS approves Mounjaro through a tier 3 specialist weight management service, your healthcare team will assess your complete medical history, including any eye problems or diabetes complications. If you have diabetes, you may be asked about your current eye screening status — the NHS recommends annual diabetic eye screening for all adults with diabetes.
Temporary vision changes (blurred vision, floaters, or difficulty focusing) during the first few weeks of Mounjaro can occur due to rapid blood sugar changes, not the medication itself. Always report any vision changes to your GP immediately. If you experience sudden vision loss, flashing lights, or a dark area in your vision, seek urgent medical attention at your nearest eye clinic or A&E. Use our free BMI calculator and discuss your full health profile with your prescriber before starting any weight loss medication.
Q1: Can Mounjaro cause blindness directly? A1: No. Mounjaro itself does not cause blindness. However, rapid blood sugar changes whilst taking it can temporarily worsen pre-existing diabetic retinopathy (eye damage from diabetes). This is why NHS prescribers screen for diabetes and eye health before prescribing. If you have diabetes, gradual blood sugar management during treatment is important. Q2: Who is at highest risk of vision problems with Mounjaro? A2: People with type 2 diabetes or pre-existing diabetic retinopathy are at higher risk of temporary vision changes if blood sugar drops too quickly. This is why NHS specialists ask about your diabetes history and may recommend eye monitoring. People without diabetes have negligible vision risk from Mounjaro. Q3: What vision changes should I report to my GP? A3: Report immediately: blurred vision, floaters, flashing lights, difficulty focusing, dark spots in vision, or sudden vision loss. These may indicate diabetic retinopathy worsening or a separate eye emergency. Do not wait — contact your GP or attend A&E if changes are sudden or severe. Q4: Does the NHS monitor vision whilst taking Mounjaro? A4: Yes, your GP will monitor you during Mounjaro treatment, especially if you have diabetes. Your prescriber may recommend continued diabetic eye screening (which is annual in the UK anyway for people with diabetes). Always attend your GP appointments and report any changes. Q5: Should I avoid Mounjaro if I have diabetes? A5: Not necessarily, but careful medical assessment is required. Many people with diabetes take weight loss medications safely under NHS supervision. Your GP and specialist will weigh the benefits of weight loss against individual eye health risks and recommend the safest approach for your situation.- 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.
What is BMI and how is it calculated?
BMI (Body Mass Index) is calculated by dividing your weight in kilograms by your height in metres squared. It's the standard screening tool used by the NHS to assess whether adults are a healthy weight.
Is BMI accurate for everyone?
BMI is a useful screening tool but doesn't account for muscle mass, bone density, or body fat distribution. Athletes may have a high BMI without excess fat. The NHS recommends using BMI alongside waist circumference for a more complete picture.
What are GLP-1 medications like Mounjaro and Wegovy?
GLP-1 receptor agonists are prescription medications that mimic gut hormones to reduce appetite and help with weight loss. Mounjaro (tirzepatide) and Wegovy (semaglutide) are the two most widely used for weight management in the UK.
Am I eligible for GLP-1 weight loss medication in the UK?
Generally, you need a BMI of 30+ (obese) or 27+ with a weight-related health condition. You must be 18 or over. Use our BMI calculator to check.
What is the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP/GLP-1 agonist with up to 22.5% weight loss. Wegovy (semaglutide) is GLP-1-only with up to 15-17% weight loss. Both are weekly injections.
Is this website free to use?
Yes, 100% free. No sign-up required. All tools work instantly in your browser and no personal data is stored on our servers.
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.