GLP-1s and eye health: what you need to know

What are its common side-effects?

The most common side-effects include stomach and digestion (nausea, diarrhoea, vomiting, constipation, stomach cramps, bloating, heartburn and burping).

Some people have headaches, dizziness, low blood sugar and hair loss, and may also feel weak or tired.

Serious but much less frequently occurring side-effects include thyroid tumours, including cancer, inflammation of pancreas, gall bladder problems, hypoglycemia (low blood sugar), especially if taking diabetes medication, kidney problems (from dehydration), stomach problems and increased heart rate, as well as eye conditions such as age-related macular degeneration and non-arteritic anterior ischemic optic neuropathy (NAION), see below for more on these.

Before taking GLP-1s

There are estimates that up to a million people are buying GLP-1s online or through private sector providers.

People who are considering any changes in their medications, including starting to take (or stopping) GLP-1s, should always talk to their GP first. They should remember the importance of nutrition, muscle preservation through exercise and the risk of weight regain on stopping GLP-1 medication.

Based on their personal health evaluation their doctor can guide them on what is best for their health and any medical conditions. Our general guidance is:

• Work with your doctor to get the basics right: blood pressure, blood sugar, cholesterol, smoking, and especially screening and treatment for sleep apnoea.

• Stay hydrated and avoid sudden large drops in blood pressure overnight if you are on blood pressure tablets; your prescriber can help adjust doses if needed.

• Have an eye examination with an optometrist, to pick up early diabetic eye disease and other conditions you may not yet know about.

• For NAION risks specifically: The factors in the first bullet point are all associated with an increased risk of developing NAION. An eye check will also check the optic nerves and see whether you have a ‘crowded’ optic disc that might put you at higher risk of NAION. If you’ve already had NAION in one eye, the other eye is at higher risk; specialists may discuss alternatives to GLP 1s. If at any time you experience sudden vision loss in one eye, get it checked urgently. It may be nothing, but with NAION, prompt assessment really counts. Although there is no treatment to reverse it, it's important to confirm the diagnosis, rule out other serious causes and protect the other eye.

Protecting your eyes while taking GLP-1 medicines?

All patients should: be aware of your eye health and seek medical advice immediately if you experience:

• Sudden vision loss

• New blind spots

• Distortion of vision

• Persistent flashing lights or floaters

• Double vision

If you are diabetic and taking GLP-1s, you should attend your regular screening appointments.

Unlike diabetic patients, patients taking GLP-1s for weight loss only are not eligible for free routine NHS diabetic eye screening.

For most people, no additional eye monitoring is required solely because they are taking a GLP-1 medicine, though regular tests are always advised as they can detect the onset of irreversible eye conditions before you experience any symptoms. If you already have an eye condition or have concerns about your eye health, speak to your optometrist, GP, or ophthalmologist.

Diabetes and eye health

People with diabetes have a greater risk of developing eye conditions such as:

• Diabetic retinopathy

• Diabetic macular oedema

• Cataracts

• Glaucoma

Any patient with diabetes, including those who are taking GLP-1s, should continue to attend their regular monitoring and screening appointments to ensure their eye health is maintained.

GLP1 RA and Diabetic Retinopathy

Diabetes can have a wide range of impacts on your health, including on your eye health.

People with diabetes are already at increased risk of developing eye conditions such as:

• Diabetic retinopathy

• Diabetic macular oedema

• Cataracts

• Glaucoma

Every adult UK patient with diabetes is invited for diabetic eye screening to check for changes to the back of the eye (retina) as progression of diabetic retinopathy or diabetic macular oedema can affect your vision.

Clinical trials have not demonstrated a conclusive association between GLP-1 RAs and diabetic retinopathy, though some have indicated this.

Therefore, the current recommendation is that any patient with diabetes, including people taking GLP-1s, should have a baseline diabetic eye screening test and attend their regular monitoring appointments to monitor their eye health.

Glaucoma

Glaucoma is a group of conditions that damage the optic nerve and lead to irreversible sight loss if untreated.

Most studies have shown that GLP-1 medications offer a small degree of protection against glaucoma. The evidence is not yet strong enough to have affected clinical practice or guidance, and further research is ongoing.

Idiopathic Intracranial Hypertension (IIH)

IIH is a build-up of pressure around the brain with an unknown cause. The symptoms can include severe and constant throbbing headaches and temporary losses of vision.

The evidence base is small, but patients taking GLP-1s reported fewer headaches and a decrease in intra-cranial pressure.

Age-related macular degeneration

Age-related macular degeneration (AMD) is a progressive condition affecting the central part of the retina responsible for detailed vision (macula). It can cause blurry vision and central vision loss. There are two types of AMD:

• Dry AMD (or early-stage AMD) has no cure. Treatment focuses on minimising its effects on patient’s lives.

• Wet AMD occurs when abnormal blood vessels grow under the retina. They leak fluid that damages the cells of the retina. Wet AMD can often be controlled with injections into the eye.

Some studies have suggested a link between GLP-1s and an increased risk of wet AMD, but this is not yet proven.

Non-Arteritic Anterior Ischemic Optic Neuropathy (NAION)

NAION’s symptoms are a sudden and painless loss of vision, usually only in one eye. This happens because the blood flow to the optic nerve has been reduced, and it causes irreversible damage.

It is rare, but disproportionately affects those over 50, with vascular conditions (e.g. high blood pressure), smokers, diabetics and those with a specific shape of optic nerve (‘crowded’ optic discs). Up to 1 in 10,000 people taking GLP-1s could be affected. This additional risk was first highlighted in 2024, and studies generally show the risk increases by a factor of two to four, though some have shown more, and others none. All studies have been based on analysis of people who have experienced NAION – prospective research is needed to confirm these findings.

In February 2026, the UK Medicines and Healthcare products Regulatory Agency (MHRA) issued guidance for clinicians regarding the risk of NAION for those taking semaglutide medicines. They advised that patients taking semaglutides with sudden loss of rapidly worsening vision should be treated as an emergency and should attend their local eye casualty or A&E.

For many patients with obesity and Type 2 diabetes, the benefits of treatment will outweigh this small potential risk. Patients considering or taking GLP-1 medicines for weight loss should discuss the benefits and risks with their healthcare professional prescribing the medication, to make sure every patient has an individual assessment.

Although NAION is rare, sudden loss of vision should always be treated as an emergency and urgently assessed by an eye specialist.

Author: Ms Sharon Heng - Moorfields consultant ophthalmic surgeon 

September 2026