Men who regularly use tadalafil, a widely prescribed medication for erectile dysfunction and urinary symptoms caused by an enlarged prostate, may face a slightly higher risk of developing glaucoma, according to a new study.
The findings, published in the British Journal of Ophthalmology, suggest that the potential increase in risk is relatively small in absolute terms. Researchers also stressed that the study does not establish that tadalafil causes glaucoma and should not be interpreted as evidence that sexual activity or occasional use of the medication causes blindness.
Tadalafil is commonly sold under the brand name Cialis and belongs to a class of medicines known as phosphodiesterase type 5 (PDE5) inhibitors. Sildenafil, marketed as Viagra, is another widely used drug in the same class.
For the study, researchers analysed anonymised health records from the TriNetX Analytics Network, focusing on 36,927 men aged 40 and older who had no previous diagnosis of glaucoma and had been prescribed tadalafil regularly for at least three months.
The researchers compared them with an equal number of men who had not used PDE5 inhibitor medicines. The groups were matched for several factors that could influence the risk of glaucoma, including age, smoking status, existing medical conditions and other medications. Participants' medical records were followed for as long as five years.
By the end of the five-year period, glaucoma had been diagnosed in 3.93 per cent of men who regularly used tadalafil, compared with 3.16 per cent of those who did not use the drugs.
In relative terms, that represented a 22 per cent higher risk among tadalafil users. But the difference in absolute terms was less than one percentage point — equivalent to roughly 77 additional cases for every 10,000 men.
That also means that the overwhelming majority of men in both groups did not develop glaucoma during the study period.
The researchers found similar increases in the likelihood of certain related eye conditions. Men taking tadalafil were about one-third more likely to develop elevated pressure inside the eye, primary open-angle glaucoma, or require treatment for glaucoma.
However, the study found no significant increase in the risk of low-tension glaucoma or primary angle-closure glaucoma.
Glaucoma is not a single disease but a group of eye disorders that can damage the optic nerve, the structure responsible for transmitting visual information from the eye to the brain. If left untreated, the damage can result in permanent loss of vision.
One of the challenges with glaucoma is that it can develop gradually and without noticeable symptoms, particularly in its early stages. This is why eye examinations can be important for detecting the disease before substantial vision loss occurs.
Why tadalafil could affect the eyes
The researchers said there are biological reasons why tadalafil could potentially influence eye health.
PDE5, the enzyme targeted by tadalafil, is found not only in tissues involved in erectile and urinary function but also in parts of the eye, including the retina, blood vessels supplying the eye, structures involved in producing aqueous humour and the optic nerve.
Aqueous humour is the clear fluid that circulates through the front portion of the eye. Its production and drainage help regulate pressure inside the eye.
One possible explanation is that tadalafil could alter blood flow in the eye or affect the production or drainage of aqueous humour, potentially influencing intraocular pressure.
The researchers cautioned, however, that the biological relationship is complicated. Some effects of PDE5 inhibition could potentially promote fluid drainage rather than increase pressure.
As a result, the precise mechanism that might connect regular tadalafil use with glaucoma remains uncertain.
Study does not prove tadalafil causes glaucoma
The researchers emphasised an important limitation: the study was observational.
That means the researchers identified an association between regular tadalafil use and glaucoma diagnoses, but they could not establish that tadalafil itself caused the disease.
The study relied on medical records and diagnosis codes rather than direct clinical measurements of participants' eyes. Researchers did not have individual measurements of eye pressure, visual fields or detailed assessments of changes to the optic nerve.
They were also unable to determine precisely how much tadalafil each participant took or calculate each individual's total exposure to the medicine over time.
Another possible explanation is that regular tadalafil users may have more frequent interactions with healthcare professionals. Greater contact with the healthcare system could increase the likelihood that an otherwise unnoticed eye condition would be detected.
These limitations mean that the findings require further investigation before a direct cause-and-effect relationship can be established.
What patients should do
The findings do not provide a reason for patients to stop taking prescribed tadalafil without first speaking to their doctor.
For men who use tadalafil regularly, particularly those who already have glaucoma or elevated eye pressure, it may be appropriate to discuss eye health and monitoring with a healthcare professional.
The same may apply to people with other recognised risk factors for glaucoma, including severe short-sightedness or a family history of the disease.
The study therefore adds to the evidence surrounding the possible effects of PDE5 inhibitors on the eye, but it does not establish that tadalafil inevitably leads to glaucoma or significant vision loss.
For patients, the key issue is the distinction between relative and absolute risk: while the study observed a statistically higher risk among regular tadalafil users, the overall difference between the groups was small, and most men studied did not develop glaucoma.