This randomized controlled trial evaluated the efficacy and safety of once-daily tadalafil (TAD-OaD) in 590 men with erectile dysfunction (ED) who had partial responses to as-needed phosphodiesterase type-5 inhibitors (PDE5Is) such as sildenafil, tadalafil, or vardenafil. After a 4-week open-label PRN-PDE5I lead-in and a washout period, participants were randomized to
