Tadalafil is a pyrazinopyridoindole, specifically 2,3,6,7,12,12a-hexahydropyrazino[1',2':1,6]pyrido[3,4-b]indole-1,4-dione, substituted at position 2 with a methyl group and at position 6 with a 1,3-benzodioxol-5-yl group (the 6R,12aR-diastereomer). It is a phosphodiesterase V inhibitor, marketed as Cialis for erectile dysfunction and as Adcirca for pulmonary arterial hypertension. It functions as an EC 3.1.4.35 (3',5'-cyclic-GMP phosphodiesterase) inhibitor and a vasodilator, and is classified as a pyrazinopyridoindole and a benzodioxole.
