Tadalafil is one of the original boner drugs. It is a phosphodiesterase 5 (PDE5) inhibitor which prevents an enzyme called phosphodiesterase type-5 from causing an erection to go down sooner than it otherwise might. Tadalafil can only help to maintain an erection if the penis is physically stimulated, eg by hand, mouth or during intercourse. Tadalafil is also effective in treating benign prostatic hyperplasia (BPH) which is caused by an enlarged prostate and can effect an older man’s ability to urinate, causing his flow to be only a fraction of what it was when he was in his twenties. It is also used in both men and women to help treat pulmonary arterial hypertension. It does this by inhibiting the PDE5 enzyme in the lungs which in turn helps relax the blood vessels and allows a person to breath better during exercise and exertion.