Tadalafil is a pyrazinopyridoindole that is 2,3,6,7,12,12a-hexahydropyrazino[1′,2′:1,6]pyrido[3,4-b]indole-1,4-dione substituted at position 2 by a methyl group and at position 6 by a 1,3-benzodioxol-5-yl group (the 6R,12aR-diastereomer). A phosphodiesterase V inhibitor inhibitor, currently marketed in pill form for treating erectile dysfunction under the name Cialis; and under the name Adcirca for the treatment of pulmonary arterial hypertension. It has a role as an EC 3.1.4.35 (3′,5′-cyclic-GMP phosphodiesterase) inhibitor and a vasodilator agent. It is a pyrazinopyridoindole and a member of benzodioxoles.
