When changing treatment to tadalafil, patients administered the drug earlier in the day and over a broader period of time. A total of 2, men mean age PDE5Is probably cause a small increase in the risk of non-arteritic ischemic optic neuropathy. Changes in behavior of long-term sildenafil users were evaluated by assessing time of dose relative to sexual intercourse attempts during treatment with sildenafil and tadalafil. Sex Med Rev ;6: Following the dosing instructions reflecting tadalafil's extended period of effectiveness, men with a history of established sildenafil use changed their dose-attempt behavior when treated with tadalafil. Previous article in issue. Keywords used for the search were erectile dysfunction, phosphodiesterase type 5 inhibitors, sildenafil, vardenafil, tadalafil, avanafil, safety, side effects, and adverse events, among others. Main Outcome Measures Visual, auditory, cardiovascular, renal, hepatic, priapic, and oncologic outcomes associated with the intake of PDE5Is for the treatment of ED, in addition to drug interactions, abuse, overdose, and the phenomenon of counterfeit medications. Similar daily cycles of frequency of dosing and intercourse attempts were observed in all study periods and were characterized by a small peak in the morning and a large peak in the evening. There appears to be an association between PDE5I use and melanoma but the absence of a mechanism of causation raises doubt that the association is cause and effect. PDE5I abuse and use of counterfeit medications present serious global health concerns. The possibility that PDE5Is cause sensorineural hearing loss remains uncertain. Tadalafil, a phosphodiesterase type 5 inhibitor, has an extended period of effectiveness, up to 36 hours, for the treatment of erectile dysfunction ED.