Tadalafil is a drug best known for the treatment of erectile dysfunction in men. Tadalafil as compared to sildenafil citrate, the two drugs act similarly and help patients overcome male impotence. Sildenafil (Generic ), Vardenafil (Generic Levitra), and Tadalafil (Generic Cialis) all work by inhibiting PDE5, tadalafil's pharmacologic distinction is its longer half-life (17.50 hours) – compared to (4.0–5.0 hours) and Levitra (4.0–5.0 hours) – resulting in longer duration of action, and so partly responsible for "The Weekend Pill" sobriquet.