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 Side Effects: Eyes, Vision Changes & UK Access
Mounjaro (tirzepatide) is a prescription-only weight management injection that may cause vision changes or eye-related side effects in some users. While eye problems are not among the most common side effects, changes in vision or blurred eyes have been reported during clinical trials and real-world use. This guide explains what eye side effects to watch for, how to access Mounjaro in the UK, and what you can expect to pay through private prescription routes—since NHS access remains limited and varies significantly by region.
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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.
Mounjaro Eye Side Effects and Vision Changes in the UK
Vision changes linked to Mounjaro are relatively uncommon but have been reported by some users. These may include blurred vision, difficulty focusing, or temporary changes in how you see colours. In some cases, these effects settle as your body adjusts to the medication over several weeks.
If you have existing eye conditions such as diabetic retinopathy (damage to blood vessels in the retina from high blood sugar), Mounjaro may temporarily worsen vision or require closer monitoring by your eye care specialist. This is because rapid changes in blood sugar control—which Mounjaro helps achieve—can sometimes cause temporary vision fluctuations in people with diabetes-related eye disease.
When to seek urgent help: If you experience sudden vision loss, severe blurriness, flashing lights, or new floaters (spots in your vision), contact your GP or eye hospital immediately. These could indicate a more serious condition requiring emergency assessment.
Most reported eye side effects are mild and temporary, but always inform your GP or prescriber if you notice any vision changes after starting Mounjaro or increasing your dose.
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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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Accessing Mounjaro in the UK: NHS vs Private Routes & Costs
NHS access: Mounjaro is approved by NICE for use in specialist weight management services (tier 3/4), but availability varies significantly across regions. Waiting lists can be 6–18 months in many areas. You'll need a GP referral to your local specialist weight management service, which assesses your eligibility based on BMI and health conditions.
Private access: You can obtain a Mounjaro prescription through a UK-licensed online prescriber following a clinical assessment. Costs typically range from £150–£300 per month depending on your dose (higher doses cost more). A KwikPen containing 4 weekly injections usually costs between £170–£250 for the 5mg or 10mg maintenance doses. Prices vary between private providers, so it's worth comparing. Prescriptions are dispensed by GPhC-registered pharmacies. Private access removes NHS waiting lists but requires upfront payment.
To access Mounjaro privately, you'll complete an online health questionnaire reviewed by a UK-registered doctor or nurse prescriber. If approved, a prescription is issued and sent to a registered pharmacy for dispensing. The entire process typically takes 2–5 working days. You can use our free GLP-1 weight loss calculator to estimate potential results at different Mounjaro doses, which may help inform your decision. Compare private costs carefully, as pricing and service quality vary. Always check that the provider is registered with the General Pharmaceutical Council (GPhC) before proceeding.
- 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?
Permanent eye damage from Mounjaro itself is rare. Most vision changes are temporary and resolve within weeks as your body adjusts. However, if you have diabetic retinopathy or other eye disease, rapid blood sugar changes during Mounjaro treatment may require specialist monitoring. Always discuss pre-existing eye conditions with your prescriber before starting.
How much does Mounjaro cost privately in the UK?
Private Mounjaro costs typically range from £150–£300 per month depending on dose. A single KwikPen (4 weekly injections) usually costs £170–£250 for maintenance doses (5mg or 10mg). Prices vary between private providers and pharmacies. Starting doses (2.5mg) are sometimes cheaper. Ask your prescriber for an exact quote for your specific dose.
Can I get Mounjaro on the NHS?
Yes, NICE has approved Mounjaro for NHS use in specialist weight management services (tier 3/4). However, NHS access is limited and varies by region—waiting lists can be 6–18 months. You'll need a GP referral to your local specialist service. Check availability in your area by contacting your GP or local integrated care board (ICB).
What's the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, while Wegovy (semaglutide) is a GLP-1-only agonist. Clinical trials show Mounjaro may produce slightly higher average weight loss (~20% vs ~15%), but individual results vary significantly. Both are prescription-only and cost similarly in private practice. Your prescriber will assess which suits you best.
How long does Mounjaro take to work?
You may notice appetite changes within the first 2–4 weeks, but significant weight loss typically takes 8–12 weeks. Mounjaro is usually increased gradually every 4 weeks, so full effects depend on reaching your optimal dose. Weight loss continues over 6–12 months. Results vary individually. Use our free progress tracker to monitor changes over time.
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.