testosterone: an anabolic hormone that builds and maintains bone and muscle mass, skin elasticity, sex drive, and cardiovascular health in both sexes; the dominant male hormone.

You may enjoy reading Candace's blogpost for ZRT Laboratories titled:
Andropause: Real Men Go For Balance

Learn more about testosterone and it's role in a healthy sex life in Candace's blog post, Dear Libido: Why Did You Leave Me?