Tadalafil has been used in approximately 15,000 men participating in clinical trials, and over eight million men worldwide (primarily in the post-approval/post-marketing setting).
In May 2005, the U.S. Food and Drug Administration found that tadalafil (along with other PDE5 inhibitors) was associated with vision impairment related to NAION (non-arteritic anterior ischemic optic neuropathy) in certain patients taking these drugs in the post-marketing (outside of clinical trials) setting.