Study of nearly 37,000 men finds 22% increased risk over five years, but researchers say further investigation is needed.
A widely prescribed medication used to treat erectile dysfunction and urinary symptoms has been associated with a modestly higher risk of glaucoma, according to a new study from Taiwan.
Researchers examining the medical records of nearly 37,000 men over the age of 40 found that those taking tadalafil—the active ingredient in the popular erectile dysfunction drug Cialis—were more likely to develop glaucoma over a five-year period than comparable men who were not taking the medication.
The findings do not prove that tadalafil causes glaucoma, but they add to growing evidence that phosphodiesterase type 5 inhibitors (PDE5is), the class of drugs to which tadalafil belongs, may have effects on the eyes that warrant closer attention.
The researchers said doctors should be particularly mindful of patients who already have risk factors for glaucoma.
“Ophthalmic evaluation and follow-up may be considered, particularly in patients with risk factors for glaucoma,” the authors wrote in their paper, published in the British Journal of Ophthalmology.
A medication with uses beyond erectile dysfunction
Tadalafil is best known as a treatment for erectile dysfunction, but its medical uses extend beyond sexual health.
PDE5 inhibitors work partly by relaxing blood vessels and improving blood flow. The drugs were initially investigated as potential treatments for conditions including hypertension and chest pain. During clinical development, however, researchers discovered that they had a particularly notable effect on blood flow to the penis, helping men achieve and maintain erections.
That discovery helped establish PDE5 inhibitors as a major treatment for erectile dysfunction.
Today, the drugs are also prescribed for other conditions. Tadalafil, for example, can be used to treat urinary symptoms associated with an enlarged prostate, known medically as benign prostatic hyperplasia.
This distinction is important because patients taking tadalafil for urinary symptoms may use the medication differently from those taking it for erectile dysfunction. Men with urinary symptoms can take a relatively low dose every day, while erectile dysfunction patients often take a higher dose only when needed.
The Taiwanese researchers said previous investigations into the relationship between PDE5 inhibitors and glaucoma have been limited, particularly among patients taking the drugs for urinary tract problems.
What the researchers found
For the new study, investigators used a large, anonymized database containing real-world medical records.
They identified nearly 37,000 men over 40 who were taking tadalafil for urinary tract symptoms and compared them with a similar group of men who were not taking the drug.
Over five years, tadalafil use was associated with a 22% higher risk of developing glaucoma.
The medication was also associated with an increased risk of ocular hypertension—a condition in which pressure inside the eye is elevated but has not yet caused detectable damage to the optic nerve.
Ocular hypertension does not necessarily progress to glaucoma, but elevated eye pressure is an important risk factor for the disease.
Glaucoma itself refers to a group of eye diseases that damage the optic nerve, the structure responsible for transmitting visual information from the eye to the brain. If the condition progresses untreated, it can result in permanent vision loss.
Although elevated pressure inside the eye is a major risk factor, glaucoma can also occur in people whose eye pressure falls within the normal range.
The increase in risk was relatively small
Despite the 22% relative increase reported in the study, the absolute difference between the groups was considerably smaller.
Among men over 50, 3.93% of those taking tadalafil developed glaucoma over five years, compared with 3.16% of those who did not take the drug.
That represents an absolute difference of 0.77 percentage points.
In other words, while the statistical association was significant enough to attract attention, the vast majority of tadalafil users in the study did not develop glaucoma during the five-year observation period.
The findings therefore should not automatically be interpreted as evidence that tadalafil is dangerous for most people who use it.
An association is not proof of cause
Because the research was based on medical records rather than a randomized clinical trial, it cannot establish that tadalafil itself caused the additional cases of glaucoma.
People who take tadalafil may differ from people who do not take it in ways that could influence their risk of developing eye disease. Researchers can use statistical methods to account for known differences, but observational studies cannot eliminate every possible source of confounding.
The findings also do not necessarily establish what the risk might be for every tadalafil user.
The study specifically examined men taking tadalafil for urinary tract symptoms, meaning its results should not automatically be applied to people who take the drug occasionally for erectile dysfunction.
Why doctors are paying attention
The potential connection between PDE5 inhibitors and eye problems is not entirely new.
Previous research has investigated possible associations between these medications and various visual complications. The biological mechanism behind a possible relationship with glaucoma, however, remains uncertain.
That uncertainty is one reason the researchers are calling for further investigation.
Glaucoma deserves particular attention because damage to the optic nerve is generally irreversible. Treatments such as medications, laser procedures and surgery can help lower eye pressure and slow or prevent further damage, but they cannot restore optic-nerve tissue that has already been lost.
Early detection is therefore crucial.
For patients who have existing glaucoma or other risk factors for the disease, the researchers suggest that eye examinations and appropriate follow-up may be worth considering when tadalafil or related medications are prescribed.
At the same time, PDE5 inhibitors remain important treatments for several medical conditions, and researchers continue to investigate whether drugs in this class could have additional therapeutic applications.
The new findings ultimately point to a need for balance: tadalafil remains a widely used medication, but its possible relationship with eye health deserves further study.
The researchers say future investigations will be needed to determine whether PDE5 inhibitors can directly contribute to the development or worsening of glaucoma—and, if so, precisely how that process occurs.