Erectile dysfunction, to some degree, affects perhaps 50% of men between the ages of 40 and 70.  The impact on quality of life as well as a man’s sense of well being is truly staggering.  With the introduction of sildenafil citrate (Viagra) in 1998, the approach and treatment of men with ED changed dramatically.  It was no longer  necessary to subject most men to extensive and costly diagnostic testing and often embarrassing face to face encounters in order to safely offer them treatment.  But how do Viagra and the other ED drugs work exactly?  They work their magic by inhibiting a specific enzyme called phosphodiesterase 5 (PDE5).  OK, here’s what happens:  during sexual stimulation, nitric oxide (NO) is released into the tissues of the penis. NO then causes an increase in cyclic GMP which allow the erectile tissues of the penis to engorge with arterial blood, while the venous drainage of the blood slows down.The ED drugs block the breakdown of cGMP, which allows it to do its job more efficiently and powerfully.  While that might be “too much information,” it’s good to know what medications really do.  And besides, now you know more about the mechanism of action of the ED medications than most physicians!