Tadalafil should be taken orally. This medicine is used for therapy of erectile dysfunction, or impotence, consisting in lacking of ability to reach and keep in existence a penile erection. The drug class, which Tadalafil belongs to, is called inhibitors. (Viagra) and (Levitra) belong to this drug class too. When a penis is filling up with blood there a penile erection springs up. The blood vessels, which are responsible for bringing blood to male reproductive organs, extend in size what causes filling the penis up with large quantity of blood. While the blood vessels, responsible for blood away from the penis, diminish in size, what causes taking much less blood away from the penis than under usual circumstances. Sexual excitement leading to a sterling erection determines the production and ejection of nitric oxide in the male genital organs. The nitric oxide provokes the production of an enzyme called guanylate cyclase that is a necessary condition for production of cyclic guanosine (cGMP). This chemical compound controls extending and reducing of the size of the blood vessels that transport blood to and from the male reproductive organs. These changes of sizes condition erection.

Afterwards one more enzyme, which is called phosphodiesterase-5, demolishes the cGMP what makes blood vessels take their usual sizes, blood go away from the penis and thus the erection is over. Mechanism of action of Tadalafil consists in preventing phosphodiesterase-5 to ruin cGMP so the last one exists longer. The extended thus life of cGMP makes blood flow to the penis for longer period of time. The U.S. FDA approved Tadalafil in November, 2003.