The male sex hormone - testosterone

Androgens - testosterone and androstenedione - are the primary sex hormones in men. They are responsible for male secondary sex characteristics, such as a low voice and facial hair, as well as sexual function and fertility. Later in life, testosterone is responsible for the biological drive or "urge" to have sex in both men and women.

Testosterone is often called the male sex hormone because it is found naturally in higher concentrations in men than in women. However, it is responsible for libido, sexual thoughts and fantasy, and frequency of sexual activity in both genders. There is no doubt that testosterone is linked to sexual impulses. The efficacy and value of testosterone replacement therapy (TRT) in improving sexual function, however, is up for debate. Since both natural levels of testosterone and effects of TRT vary greatly by gender, we'll discuss men and women separately.

Between the ages of forty-five and fifty, men's testosterone levels naturally begin to decline. For certain individuals, this reduction can have a significant impact on sexual fitness. If their testosterone levels are abnormally low, men will first experience a drop in libido and eventually have difficulty reaching orgasm. When they do reach orgasm, the volume of ejaculate may be smaller. Low testosterone levels may result in impaired fertility. In addition, lack of testosterone may decrease muscle strength and stamina and bring on depressivelike symptoms.