Andropause, also known as testosterone deficiency syndrome, is a condition in older men characterized by measurably low testosterone levels and clinical symptoms mostly of a sexual nature, including decreased desire for sex, fewer spontaneous erections, and infertility. It is a gradual decrease in testosterone levels and the development of symptoms, unlike menopause in women. The decrease in testosterone is an important factor in men suspected of having andropause. However, as men age, not only does the body start making less testosterone, but also the levels of another hormone called sex hormone binding globulin (SHBG), which pulls usable testosterone from the blood, begins to increase. Some symptoms associated with low testosterone levels include low sex drive, fatigue, reduced muscle mass, irritability, mood swings, erectile dysfunction, and depression. It is important to note that andropause is not the male equivalent to female menopause, and not all men experience it. A diagnosis of late-onset hypogonadism can usually be made based on symptoms and the results of blood tests used to measure testosterone levels. Treatment for andropause may include testosterone replacement therapy, but the risks and benefits of doing this should be considered before starting therapy.