Testosterone
"I'm a 31 year old male diabetic and was having problems with erectile dysfunction.  I started on a Cialis regimen and it only slightly helped.  My urologist then tested me for Testosterone and found I was in the low 200 range.  He gave me a month supply and a prescription for Testim.  The first month there didn't seem too much impact, but by the second month I had both more energy and sex drive. The erectile dysfunction problem was greatly reduced and in some cases the Cialis isn't needed.

As a side note, some people complain about the smell.  I think it just smells like cheap aftershave, but doesn't really bother me.  My girlfriend and two of my close friends that are also female think it smells wonderful.  I'm not sure if it a pheromone response or just pleasing to them."