Some myths refuse to die, especially when they mix sex and shame.For generations, young people were warned that sexual activity could make them blind. Science has long dismissed the claim. But a new study has brought the old myth back in an unexpected form.This time, sex is not under suspicion. A pill is.Tadalafil, best known by the brand name Cialis, is widely used to treat erectile dysfunction, or difficulty getting or maintaining an erection. It is also prescribed regularly for urinary problems associated with an enlarged prostate.Now, a large study has linked long-term tadalafil use to an increased risk of glaucoma, a group of eye diseases where optic nerve damage causes vision loss.The reassurance: The study does not show that sex harms the eyes or that occasional tadalafil use causes blindness.The study focused on men over 40 who regularly took tadalafil for urinary symptoms, such as frequent or urgent urination or a weak stream.Researchers used the TriNetX Analytics Network, a platform containing anonymized health records from across 21 countries. Its scale let them search for an uncommon pattern beyond a single hospital.They identified 36,927 men aged 40 or older who had no previous glaucoma diagnosis and had been prescribed regular tadalafil for at least 3 months. They were compared with 36,927 matched men who had used no drug from the same family.The groups were matched for factors that could influence glaucoma risk, including age, smoking, health conditions, and other medications. Their health records covered up to five years.Over five years, glaucoma appeared in roughly four of every 100 tadalafil users, compared with about three of every 100 non-users. The precise rates of diagnosis in each group were 3.93 percent and 3.16 percent, respectively, over the five-year period.Researchers described that difference as a 22 percent increase in relative risk. It sounds dramatic, but the gap between the two groups was less than one percentage point: equivalent to about 77 additional diagnoses for every 10,000 men. Most men in both groups did not develop glaucoma.