Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist licensed in the UK for type 2 diabetes management. Whilst highly effective at lowering blood glucose and HbA1c, concerns have emerged regarding Mounjaro and diabetic retinopathy, particularly in patients with pre-existing eye disease. Clinical trial data suggest that rapid glucose reduction—rather than the medication itself—may temporarily worsen retinopathy in susceptible individuals. Understanding this relationship is essential for safe prescribing, appropriate patient selection, and timely ophthalmology monitoring to prevent vision-threatening complications.

Understanding Mounjaro (Tirzepatide) and Its Use in Diabetes

Mounjaro (tirzepatide) is a dual glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) receptor agonist licensed in the UK for adults with type 2 diabetes. It is indicated as an adjunct to diet and exercise when other treatments provide inadequate glycaemic control.

The medication works by mimicking the action of incretin hormones, which are naturally released after eating. By activating both GIP and GLP-1 receptors, Mounjaro enhances insulin secretion when blood glucose levels are elevated, suppresses inappropriate glucagon release, slows gastric emptying, and promotes satiety. These combined effects improve glycaemic control and can lead to weight reduction, both important therapeutic goals in type 2 diabetes management.

Mounjaro is administered once weekly via subcutaneous injection, typically in the abdomen, thigh, or upper arm. The starting dose is 2.5 mg weekly, with gradual titration every four weeks based on glycaemic response and tolerability, up to a maximum of 15 mg weekly. In the SURPASS clinical trials, tirzepatide demonstrated substantial reductions in HbA1c and body weight compared to placebo and active comparators.

In the UK, NICE guidance recommends tirzepatide as an option for treating type 2 diabetes in line with current recommendations for GLP-1 receptor agonists in the NICE pathway. When used in combination with insulin or sulfonylureas, there is an increased risk of hypoglycaemia, and dose adjustments of these medications may be needed.

As with all diabetes medications that produce rapid glucose lowering, careful consideration must be given to potential complications, particularly in patients with pre-existing microvascular disease such as diabetic retinopathy. Mounjaro is not indicated for use in type 1 diabetes or diabetic ketoacidosis.

What Is Diabetic Retinopathy and Why Does It Matter?

Diabetic retinopathy is a microvascular complication of diabetes mellitus and remains one of the leading causes of preventable blindness in working-age adults in the UK. It develops when chronically elevated blood glucose levels damage the small blood vessels in the retina—the light-sensitive tissue at the back of the eye responsible for vision. The condition progresses through distinct stages, from mild non-proliferative changes to severe proliferative diabetic retinopathy, which can result in vision-threatening complications.

In the early stages, known as non-proliferative diabetic retinopathy (NPDR), patients may experience microaneurysms, retinal haemorrhages, and exudates but often remain asymptomatic. As the disease advances, retinal ischaemia triggers the growth of abnormal new blood vessels—a process called neovascularisation. This proliferative diabetic retinopathy (PDR) carries significant risks, including vitreous haemorrhage, tractional retinal detachment, and neovascular glaucoma, all of which can lead to severe visual impairment or blindness if untreated.

Diabetic macular oedema (DMO) can occur at any stage and involves fluid accumulation in the macula, the central part of the retina responsible for sharp, detailed vision. DMO is a leading cause of visual loss in people with diabetes and requires prompt ophthalmological intervention, often with intravitreal injections or laser therapy.

The NHS Diabetic Eye Screening Programme offers annual retinal photography to all people aged 12 and over with diabetes, enabling early detection and timely referral to ophthalmology services. In the UK screening programme, retinopathy is graded using R0-R3 (for retinopathy) and M0-M1 (for maculopathy) categories, which determine referral pathways and follow-up intervals.

Effective glycaemic control, blood pressure management, and lipid optimisation are fundamental to preventing or slowing the progression of diabetic retinopathy. However, research from the Diabetes Control and Complications Trial (DCCT) has shown that rapid improvements in blood glucose control can be associated with transient worsening of retinopathy—a phenomenon that has gained renewed attention with the introduction of highly effective glucose-lowering agents.

The Link Between Mounjaro and Diabetic Retinopathy: What the Evidence Shows

The relationship between Mounjaro (tirzepatide) and diabetic retinopathy is complex and requires careful interpretation of clinical trial data. During the pivotal SURPASS clinical trial programme, which evaluated tirzepatide across diverse patient populations with type 2 diabetes, retinopathy-related adverse events were reported in a small proportion of participants. Importantly, these events were more frequently observed in patients with pre-existing diabetic retinopathy at baseline and in those achieving rapid and substantial reductions in HbA1c.

This phenomenon is not unique to tirzepatide. A well-established concept in diabetology is 'early worsening' of diabetic retinopathy, which can occur when blood glucose levels are lowered quickly after a prolonged period of poor glycaemic control. This was notably observed in the Diabetes Control and Complications Trial (DCCT) with intensive insulin therapy and more recently in the SUSTAIN-6 trial with semaglutide, another GLP-1 receptor agonist. The proposed mechanism involves rapid normalisation of retinal blood flow and metabolic changes that temporarily exacerbate ischaemia and vascular permeability before longer-term benefits accrue.

Current evidence does not suggest that tirzepatide directly causes diabetic retinopathy in patients without pre-existing disease. Rather, the observed retinopathy complications appear to be related to the magnitude and speed of glucose reduction, particularly in vulnerable individuals. In the SURPASS trials, the overall incidence of retinopathy events remained low.

The Mounjaro Summary of Product Characteristics (SmPC) advises that patients with diabetic retinopathy should be monitored closely during tirzepatide treatment. Healthcare professionals should exercise caution when initiating Mounjaro in patients with moderate to severe non-proliferative or proliferative diabetic retinopathy, particularly if glycaemic control has been suboptimal for an extended period.

Risk Factors and Monitoring Recommendations for Patients on Mounjaro

Identifying patients at higher risk of retinopathy progression when starting Mounjaro is essential for safe prescribing. Key risk factors include:

• Pre-existing diabetic retinopathy, particularly moderate to severe non-proliferative or proliferative disease

• Prolonged poor glycaemic control (HbA1c >75 mmol/mol or 9%) prior to treatment initiation

• Rapid anticipated HbA1c reduction (>2 percentage points within 3–6 months)

• Long duration of diabetes (typically >10 years)

• Concurrent hypertension or chronic kidney disease, which independently increase microvascular risk

For patients in these high-risk categories, consider a pre-treatment ophthalmology assessment before initiating Mounjaro, even if recent screening has been undertaken. This allows for baseline documentation of retinopathy status and facilitates appropriate monitoring during the early treatment phase.

Monitoring recommendations for patients on tirzepatide should align with NICE guidance on diabetes management and include:

• Annual diabetic retinopathy screening via the NHS programme for all patients, with follow-up intervals determined by the DESP grading and ophthalmologist recommendations for those with known retinopathy

• Gradual dose titration to minimise the rate of HbA1c reduction, particularly in patients with baseline HbA1c >86 mmol/mol (10%)

• Regular review of glycaemic control, blood pressure, and renal function as per NICE guidance

• Patient education on warning symptoms of retinopathy progression, including new floaters, flashing lights, visual field loss, or sudden vision changes

Healthcare professionals should document baseline retinopathy status in the clinical record and communicate with ophthalmology services when initiating Mounjaro in high-risk individuals. Collaborative care between primary care, diabetes specialist teams, and ophthalmology is essential to optimise outcomes and minimise the risk of vision-threatening complications.

Clinical Guidance: When to Seek Ophthalmology Review

Prompt recognition of retinopathy progression and timely referral to ophthalmology services are critical to preventing irreversible visual loss in patients taking Mounjaro. Patients should be advised to seek urgent medical attention if they experience any of the following symptoms:

• Sudden onset of floaters or 'cobwebs' in the vision, which may indicate vitreous haemorrhage

• Flashing lights or photopsia, suggesting retinal traction or impending detachment

• A curtain or shadow across the visual field, which may represent retinal detachment

• Sudden blurring or loss of central vision, potentially indicating macular oedema or ischaemia

• Distortion of straight lines (metamorphopsia), which can be an early sign of macular pathology

In the context of initiating or up-titrating Mounjaro, ophthalmology referral timing should follow NHS Diabetic Eye Screening Programme and local pathways:

• Proliferative diabetic retinopathy (PDR) requires urgent referral, often within 1-2 weeks, or same-day assessment if acute symptoms are present

• Suspected centre-involving diabetic macular oedema with visual symptoms warrants urgent assessment

• Moderate to severe non-proliferative diabetic retinopathy identified on screening should be referred according to local DESP pathways

• Any worsening of retinopathy during Mounjaro treatment should prompt ophthalmology review

For patients without known retinopathy but with multiple risk factors (long diabetes duration, poor baseline control, hypertension), ensure up-to-date DESP screening and consider a pre-treatment ophthalmology assessment to establish a baseline.

GPs and diabetes specialist nurses play a vital role in safety-netting by ensuring patients understand these warning signs and know how to access urgent eye care services. In England, patients can self-refer to local urgent eyecare services (such as CUES or equivalent pathways), contact NHS 111, or attend emergency eye departments depending on local arrangements. Clear documentation of retinopathy status and communication with ophthalmology colleagues when prescribing Mounjaro in high-risk patients supports integrated, patient-centred care and reduces the risk of preventable visual complications.

Frequently Asked Questions About Mounjaro and Eye Health

Does Mounjaro cause diabetic retinopathy?

Current evidence does not show that Mounjaro directly causes diabetic retinopathy in patients without pre-existing eye disease. However, like other highly effective glucose-lowering medications, rapid improvements in blood sugar control can temporarily worsen existing retinopathy in susceptible individuals. This phenomenon, known as 'early worsening', is related to the speed and magnitude of HbA1c reduction rather than a direct toxic effect of the medication.

Should I have my eyes checked before starting Mounjaro?

All patients with diabetes should participate in the NHS annual diabetic eye screening programme. If you have known diabetic retinopathy, particularly moderate or severe disease, or if your diabetes has been poorly controlled for a prolonged period, your healthcare team may recommend an ophthalmology assessment before starting Mounjaro. This helps establish a baseline and guides monitoring during treatment.

What symptoms should I watch for while taking Mounjaro?

Be alert for new visual symptoms such as sudden floaters, flashing lights, a shadow or curtain across your vision, or sudden blurring. These may indicate retinopathy progression and require urgent ophthalmology review. Contact your GP or attend an urgent eye care service if you experience any of these changes.

Can I continue Mounjaro if I develop retinopathy?

This decision should be made collaboratively between your diabetes team and ophthalmologist, taking into account the severity of retinopathy, the benefits of continued glucose control, and alternative treatment options. In many cases, Mounjaro can be continued with closer ophthalmology monitoring and appropriate eye treatments such as laser therapy or intravitreal injections if needed.

How can I reduce my risk of eye complications on Mounjaro?

Maintain regular eye screening appointments, attend all diabetes reviews, take Mounjaro as prescribed with gradual dose increases, optimise blood pressure and cholesterol control, and report any visual changes promptly. Good overall diabetes management remains the cornerstone of preventing microvascular complications, including retinopathy.

If you experience any side effects while taking Mounjaro, including changes to your vision, you or your healthcare professional can report them via the MHRA Yellow Card Scheme at yellowcard.mhra.gov.uk.

Frequently Asked Questions