The herb Tribulus terrestris has long been heard in the folk medicine of eastern countries and a, and has been used to treat  insufficiency.  tribulus terrestris saponins has been used for erectile dysfunction. Like the drug Sildenafil citrate (Viagra),tribulus terrestris saponins is thought to enhance the action of nitric oxide, which relaxes muscles surrounding blood vessels supplying the penis. As a result, blood vessels in the penis dilate, increasing blood flow, which helps maintain an erection. The difference in how they work is that Viagra blocks an enzyme called PDE5 which destroys nitric oxide and tribulus terrestris saponins is used to make nitric oxide.