Men who take tadalafil every day for urinary symptoms caused by an enlarged prostate may have a slightly higher chance of developing glaucoma, a large study suggests.

The finding which is published in British Journal of Ophthalmology is not proof that the medicine causes the eye condition, but it adds a reason for patients with existing eye-risk factors to keep up with regular eye checks.

Tadalafil, best known by the brand name Cialis, is used both for erectile dysfunction and for lower urinary tract symptoms linked to benign prostatic enlargement.

These symptoms can include needing to pass urine often, waking at night to urinate, urgency and a weak urine stream.

For most people, the potential increase in risk appears small. The research does not mean that people should stop prescribed tadalafil without discussing it with their clinician.

A medicine used for more than erectile dysfunction

Tadalafil belongs to a group of medicines called phosphodiesterase type 5 inhibitors, or PDE5 inhibitors. The same group includes sildenafil, sold as Viagra.

These medicines improve blood flow by relaxing blood vessels. At lower daily doses, tadalafil can also ease urinary symptoms associated with benign prostatic enlargement, a non-cancerous growth of the prostate gland that becomes more common with age.

Tadalafil has been used for these purposes for many years. Its known side effects include headache, indigestion, flushing and nasal congestion. Eye-related warnings have also been recognised for PDE5 inhibitors, although serious visual complications are considered uncommon.

The new findings focus on possible longer-term eye effects among men prescribed tadalafil for urinary symptoms, rather than occasional use for erectile dysfunction.

What the study found

The study examined electronic health records from the TriNetX Analytics Network, including more than 70,000 men aged 40 and over with no previous history of glaucoma.

Researchers compared people prescribed tadalafil for urinary symptoms with similar people who were not prescribed the medicine. They followed outcomes over up to five years, looking for diagnoses of glaucoma, ocular hypertension or the start of glaucoma treatment.

Men prescribed tadalafil were reported to be:

• 22% more likely to receive a glaucoma diagnosis;
• 32% more likely to develop ocular hypertension, meaning raised pressure within the eye;
• 33% more likely to be diagnosed with primary open-angle glaucoma, the most common form of the disease; and
• 33% more likely to begin treatment for glaucoma.

In plain language, glaucoma diagnoses were somewhat more frequent in the tadalafil group. However, the difference in absolute terms was small.

What is glaucoma?

Glaucoma is a group of eye diseases that damage the optic nerve, which carries visual information from the eye to the brain. Damage is often associated with raised pressure inside the eye, although glaucoma can also occur when eye pressure is within the usual range.

Primary open-angle glaucoma develops slowly and often causes no early symptoms. Peripheral vision is commonly affected first. Because sight loss can progress gradually and cannot usually be reversed, early detection through routine eye examinations is important.

Glaucoma is a leading cause of irreversible blindness worldwide, but many people can retain useful vision when it is found early and treated.

Treatments, including eye drops, laser procedures and surgery, aim to lower eye pressure and slow further optic-nerve damage.

Why tadalafil might affect the eyes

The study was not designed to establish a biological explanation, and the precise reason for the association remains uncertain.

PDE5 inhibitors affect signalling pathways involved in blood-vessel relaxation. These pathways are present in tissues throughout the body, including blood vessels that supply the eye and optic nerve. It is possible that long-term changes in blood flow, fluid movement or pressure regulation in the eye could matter for people already prone to glaucoma.

However, this remains a hypothesis. The study did not directly measure eye pressure, optic-nerve blood flow or other biological changes before and after tadalafil treatment. It therefore cannot show that tadalafil itself triggered glaucoma.

Another possibility is that people prescribed tadalafil differed from non-users in ways not fully captured in health records. Age, diabetes, cardiovascular disease, medication use and access to eye care may all influence glaucoma risk.

How strong is the evidence?

This was a large human observational study, which is useful for identifying potential safety signals in routine clinical care. Its size and multi-year follow-up are strengths.

But observational research has important limits. It can show that two factors occur together, but it cannot reliably prove that one caused the other. Although researchers can adjust for known differences between groups, they cannot fully account for factors that are missing from medical records or difficult to measure.

The study population was also predominantly white, limiting certainty about whether the findings apply equally across other ethnic groups. This is particularly important because glaucoma risk varies between populations.

Further studies, ideally including diverse populations and detailed eye measurements, will be needed to clarify whether tadalafil contributes directly to glaucoma risk and, if so, which patients are most vulnerable.

What this means for patients

The findings should not cause alarm among people who occasionally use tadalafil for erectile dysfunction.

The concern examined in this study relates mainly to longer-term, daily treatment for urinary symptoms associated with an enlarged prostate.

People taking daily tadalafil should not stop the medicine abruptly or change their dose based on this research alone.

Untreated urinary symptoms can affect sleep, daily activities and quality of life, and tadalafil may be an appropriate option for many patients.

However, it is sensible for people taking tadalafil regularly to tell their optometrist or ophthalmologist about all medicines they use. This may be particularly relevant for those with known glaucoma, ocular hypertension, a close family history of glaucoma, severe short-sightedness, diabetes or other eye-health concerns.

Regular comprehensive eye examinations are already important for people at increased glaucoma risk. The new study supports attention to this routine monitoring rather than introducing a new universal screening programme.

Anyone who develops sudden loss of vision, marked changes in vision, severe eye pain, halos around lights, or a severe headache with nausea should seek urgent medical assessment. These symptoms can signal an acute eye problem, although they are not typical of the slow-developing open-angle glaucoma studied here.

Other options for enlarged prostate symptoms

Tadalafil is one of several treatments for urinary symptoms linked to benign prostatic enlargement. The choice depends on the severity of symptoms, prostate size, other health conditions and a person’s preferences.

Lifestyle measures, such as adjusting evening fluid intake and reducing caffeine or alcohol where relevant, can help some people. Medicines may include alpha-blockers, which relax muscles around the prostate and bladder outlet, and 5-alpha-reductase inhibitors, which can shrink the prostate over time in suitable patients.

Procedures and surgery may be considered when symptoms remain troublesome, medicines are unsuitable, or complications develop.

All options have potential benefits and side effects. A clinician can help weigh these alongside any individual risk of glaucoma or other eye disease. Always talk to your healthcare providers for medical advice.

Questions that still need answers

Researchers now need to determine whether the association is reproducible in other healthcare databases and whether it differs according to tadalafil dose, duration of use or pre-existing glaucoma risk.

Studies that include eye examinations before treatment starts, alongside regular measurements of eye pressure and optic-nerve health, could provide clearer answers. Comparisons with other medicines used for enlarged prostate symptoms may also help separate the possible effect of tadalafil from the health characteristics of people prescribed it.

The study raises a reasonable question about long-term tadalafil use and glaucoma, but it does not establish that the drug causes the condition. The apparent increase in risk was small in absolute terms, and tadalafil remains an established treatment for appropriately selected patients.

For people using tadalafil daily, particularly those with a personal or family history of glaucoma, the most practical message is to maintain routine eye care and discuss any concerns with the clinician who prescribed the medicine.