TADALAFIL 20 MGl is: the main active ingredient of Cialis and generic Cialis and is a PDE5 inhibitor, used for treating erectile dysfunction. t reacts with certain chemicals in the man's body, which reaction aids the engorgement of certain penile tissues with blood and that causes harder erection. Tadalafil 20mg is a pill, which should be taken orally with a glass of water anywhere from thirty minutes to an hour before having sex.