Regular use of tadalafil, a drug commonly prescribed to treat erectile dysfunction and urinary symptoms associated with an enlarged prostate, may be linked to a slightly increased risk of glaucoma, a new study has found.
The study, published in the British Journal of Ophthalmology, however, does not suggest that sexual activity causes blindness or that occasional use of tadalafil leads to vision loss.
Tadalafil, widely known by the brand name Cialis, belongs to a group of medicines called phosphodiesterase type 5 (PDE5) inhibitors. Sildenafil, commonly sold as Viagra, is another drug in the same class.
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Researchers examined anonymised health records from the TriNetX Analytics Network and identified 36,927 men aged 40 years and above who had no previous diagnosis of glaucoma and had been prescribed tadalafil regularly for at least three months.
They compared the men with an equal number of matched individuals who had not used drugs in the same class. The groups were matched for factors including age, smoking, existing health conditions, and other medications, with records followed for up to five years.
The researchers found that glaucoma was diagnosed in 3.93 per cent of tadalafil users during the five-year period, compared with 3.16 per cent among non-users.
Although this represented a 22 per cent increase in relative risk, the absolute difference was less than one percentage point, equivalent to about 77 additional cases for every 10,000 men. The vast majority of men in both groups did not develop glaucoma.
The researchers also observed an increased risk of some related eye problems. Tadalafil users were about one-third more likely to develop elevated eye pressure, primary open-angle glaucoma, or begin treatment for glaucoma.
However, there was no significant increase in the risk of low-tension glaucoma or primary angle-closure glaucoma.
Glaucoma refers to a group of eye conditions that damage the optic nerve and can result in permanent vision loss. The disease can develop silently, without obvious symptoms in its early stages, making regular eye examinations important, particularly among people at increased risk.
Researchers said there are possible biological explanations for the association. PDE5, the enzyme targeted by tadalafil, is present not only in tissues involved in erectile and urinary function but also in the retina, ocular blood vessels, structures involved in the production of eye fluid, and the optic nerve.
One possibility is that tadalafil could influence blood flow or the production and drainage of aqueous humour, the clear fluid in the front of the eye, potentially affecting pressure within the eye. However, the researchers noted that the biological effects are complex and could also promote fluid drainage, meaning the precise mechanism remains uncertain.
The study was observational and therefore cannot prove that tadalafil causes glaucoma. The researchers relied on medical diagnosis codes and did not have direct measurements of participants’ eye pressure, visual fields, or optic nerve changes.
They also could not establish the exact doses taken by individual patients or calculate their total exposure to tadalafil. In addition, people who regularly take the drug may have more frequent contact with healthcare services, increasing the likelihood that glaucoma would be detected.
Although the findings are not a reason for patients to discontinue prescribed tadalafil without medical advice, the experts suggested that regular users, particularly those with glaucoma, elevated eye pressure, severe short-sightedness, or a family history of glaucoma, may wish to discuss appropriate eye monitoring with their doctors.
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