Low testosterone, in men and women, can lead to infertility, loss of bone and muscle mass, and even cause emotional changes. An estimated five million American men have low testosterone. Symptoms may include a low sex drive, fatigue, erectile dysfunction/sexual disorders, and even hot flashes. While successful treatment depends upon the cause of low testosterone, it most often involves testosterone replacement therapy. Just as in men, the most predominate sex hormone in women is also Testosterone.