8. Many men are on testosterone replacement therapy to stay young, although it hasn't been proven effective or safe. Concerns include increased risk of prostate cancer and stroke. (Sound familiar?)
9. Women have testosterone, too, though only one seventh of the amount coursing through a man, and it powers our sex drives along with estrogen.
10. Two hormone-replacement pills for menopausal symptoms (Estratest and Premarin plus methyltestosterone) contain testosterone to help increase sex drive.
11. Although a few million women may be taking testosterone to increase libido, there's no long-term safety data, according to hormone expert Susan Love, MD, author of Self Nuture and one of our Lluminari experts. In fact, Love says, blood levels of testosterone are correlated with an increase in breast cancer risk.