For years, jokes and myths have claimed that sex can make people go blind. Medical science has long debunked that idea, but a new study has revived the topic from a different angle. This time, researchers are looking not at sex itself, but at a widely used erectile dysfunction medication.
Tadalafil, commonly sold under the brand name Cialis, is prescribed for erectile dysfunction and urinary symptoms associated with an enlarged prostate. A large analysis of medical records now suggests that men who use tadalafil regularly over extended periods may have a slightly higher risk of developing glaucoma.
How the study was carried out
Researchers used the TriNetX Analytics Network, a global database containing anonymized electronic health records from 21 countries. This allowed them to examine health outcomes across a large and diverse population rather than relying on patients from a single hospital or clinic.
They identified 36,927 men aged 40 and older who had no previous history of glaucoma and had been prescribed regular tadalafil for at least three months. These participants were matched with 36,927 men who did not use tadalafil or related drugs, with the groups balanced for age, smoking status, medical conditions and other medications.
Researchers followed the medical records for up to five years, looking for new glaucoma diagnoses, increased eye pressure and the initiation of glaucoma treatment. The matched design helped reduce, although not completely eliminate, the influence of potential confounding factors.
Small but measurable increase in risk
Over five years, glaucoma was diagnosed in approximately four out of every 100 men who used tadalafil, compared with around three out of every 100 men in the non-user group. The respective diagnosis rates were 3.93% and 3.16%.
Statistically, this represented a 22% relative increase in glaucoma risk among regular tadalafil users. In absolute terms, however, the difference was relatively modest: approximately 77 additional glaucoma diagnoses for every 10,000 men using tadalafil over five years.
Tadalafil users were also somewhat more likely to develop elevated eye pressure, primary open-angle glaucoma or begin glaucoma treatment. By contrast, researchers found no clear increase in low-tension glaucoma or primary angle-closure glaucoma, conditions involving different mechanisms.
Why an erection drug could affect the eyes
Tadalafil belongs to a class of medications called phosphodiesterase type 5 inhibitors, or PDE5 inhibitors, which also includes sildenafil, commonly marketed as Viagra. These drugs enhance a chemical signaling pathway that relaxes smooth muscle and widens blood vessels, increasing blood flow in particular tissues.
Although PDE5 inhibitors are best known for their effects involving the penis, prostate and bladder, PDE5 enzymes are also present in the retina, blood vessels of the eye, tissues involved in producing aqueous humor and the optic nerve head. This distribution means the medications may have effects beyond sexual and urinary function.
One proposed explanation is that tadalafil could widen blood vessels within the eye and temporarily increase production of aqueous humor, the clear fluid in the front portion of the eye. If fluid production exceeds drainage, intraocular pressure can rise, and repeated elevations over time could potentially damage the optic nerve in susceptible individuals.
The biology is complex, however, because the same signaling pathways may also facilitate fluid drainage from the eye, potentially reducing pressure under some circumstances. Tadalafil could therefore have opposing effects, and researchers do not yet know which becomes more important during long-term use.
Limits of the evidence and what it means
The researchers emphasized that the study was observational, meaning it identified an association but cannot demonstrate that tadalafil directly causes glaucoma. Cases were identified using diagnosis codes rather than detailed ophthalmological examinations, and the database did not contain measurements of intraocular pressure or optic nerve structure.
Researchers also lacked precise information about how frequently participants took the medication, changes in dosage or their total cumulative exposure. Men regularly using tadalafil might also interact with healthcare services more frequently and therefore have more opportunities for glaucoma screening and diagnosis, potentially influencing the observed association.
The findings do not mean patients should abruptly stop taking tadalafil, particularly when it is being used to manage significant erectile or urinary symptoms. Decisions about changing a prescribed medication should be discussed with a healthcare professional.
Men who use tadalafil daily or over long periods, particularly those with existing glaucoma, elevated eye pressure, severe short-sightedness or a family history of glaucoma, may wish to discuss regular eye examinations with an ophthalmologist. Early detection is important because vision loss caused by glaucoma is generally irreversible.
Glaucoma burden and future directions
Glaucoma refers to a group of eye diseases that damage the optic nerve, disrupting the transmission of visual information to the brain. It is a leading cause of irreversible blindness worldwide and can progress without noticeable symptoms until peripheral vision has already been affected.
As populations age, the number of people living with glaucoma is expected to increase substantially in coming decades. Understanding whether commonly used medications, including treatments for sexual and urinary health, influence long-term eye risk could therefore have important clinical implications.
Researchers are also investigating new technologies for glaucoma management. One potential approach involves smart contact lenses designed to continuously monitor eye pressure and release glaucoma medications when necessary. Early laboratory and animal research has produced encouraging results, although robust human trials will be required before such devices could become part of routine clinical care.
The latest tadalafil analysis, published in the British Journal of Ophthalmology, does not revive the myth that sex causes blindness. Instead, it suggests a more nuanced message: men who use certain medications regularly over long periods may benefit from paying closer attention to their vision and eye health.
