The generic term for any natural or synthetic compound, usually a steroid hormone, that stimulates or controls the development and maintenance of masculine characteristics by binding to androgen receptors. Androgens are also the original anabolic steroids. The primary and most well-known androgen is testosterone.

Androgen Deficiency (AD)

A group of symptoms that are related to low testosterone levels in the bloodstream which occur commonly in adult men. AD may be associated with: decreased sex drive (libido), erectile dysfunction (ED, inadequate erections), lowered sperm count and infertility, increased breast size and tenderness, reduced energy, symptoms similar to menopause in women (e.g., hot flashes, increased irritability, inability to concentrate, depression). With prolonged and severe decrease in testosterone, men may have loss of body hair, reduced muscle bulk and strength, brittle bones (osteoporosis), and smaller testicles.


A specially trained doctor that diagnoses diseases that affect your glands. They know how to treat conditions that are often complex and involve many systems within your body.

Erectile Dysfunction (ED) / Impotence

Consistent or recurrent inability to attain and/or maintain a penile erection sufficient for sexual performance.

Free Testosterone

Testosterone is present in the blood as “free” testosterone (2-3%) or unbound testosterone. Testosterone may be bound to either albumin (a serum protein) or to a specific binding protein called Sex Steroid Binding Globulin (SSBG) or Sex Hormone Binding Globulin (SHBG).


A clinical syndrome that results from failure of the testes to produce physiological levels of testosterone (androgen deficiency) and the normal number of spermatozoa due to disruption of one or more levels of the hypothalamic-pituitary-gonadal (HPG) axis.

Hypothalamic-Pituitary-Gonadal (HPG) Axis

The reproductive hormonal axis in men consists of three main components: (A) the hypothalamus, (B) the pituitary gland, (C) the testes. Regulation of this axis impacts on the steroid-sensitive end organs such as the prostate and penis. This axis normally functions in a tightly regulated manner to produce concentrations of circulating steroids required for normal male sexual development, sexual function and fertility.


The hypothalamus links the nervous system to the endocrine system via the pituitary gland (hypophysis). The hypothalamus is responsible for certain metabolic processes and other activities of the Autonomic Nervous System.

Pituitary Gland

An endocrine gland about the size of a pea which is a protrusion off the bottom of the hypothalamus at the base of the brain. The pituitary gland secretes hormones regulating homeostasis, including tropic hormones that stimulate other endocrine glands.

Primary Hypogonadism

Disease of the testes.

Secondary Hypogonadism

Disease of the pituitary or hypothalamus.

Testicles (Testes)

Two ovoid-shaped male reproductive organs located in the scrotum. They produce sperm and the male hormone, testosterone.


The hormone produced in men’s bodies in the testicles which affects sexual features and development.

Testosterone Replacement Therapy

Testosterone medications which are available in several forms (injection, transdermal patch, topical gel, buccal, pellet for subcutaneous implant) with the therapeutic goals of: improving and maintaining masculine characteristics, improving sex drive (libido) and erections, increasing energy and well-being, improving muscle mass and strength, and improving bone mineral density.

Total Testosterone

Total testosterone includes the percentage which is chemically bound and unavailable plus the free testosterone which is bioavailable and unbound. In the United States, male total testosterone levels below 300 to 400 ng/dl are generally considered low.


A urologist is a physician who has specialized knowledge and skill regarding problems of the male and female urinary tract and the male reproductive organs.