Androgen replacement therapy is hormone treatment for middle-aged and older men facing Hypogonadism which is often intended to counter the natural effects of aging. Androgen replacement is also used for men who have lost their testicular function to disease, or cancer, or to other causes. As men enter middle age they may notice changes caused by a relative decline in testosterone: fewer erections, fatigue, thinning skin, declining muscle mass and strength, more body fat. This dissatifaction with the changes of aging has led to the development of the idea of androgen replacement therapy.