The only side effect I get that concerns me is dependency.
I started taking ED pills to help with my performance anxiety. Make no mistake, they do work (can guarantee the best erections of my life each and every time, no matter the circumstances) but before I started taking ED pills I was able to occasionally achieve erections on my own (only experiencing the performance anxiety when under stress, or tired, etc.,.). Unfortunately, my brain has now decided that if I'm not taking an ED pill, that I SHOULD be experiencing performance anxiety and just outright refuses to allow me to have an erection.