Glossary
Definitions in plain language, with links to the articles that go deeper.
Anabolic-androgenic steroids (AAS)
Synthetic hormones derived from testosterone that promote muscle and bone growth (anabolic effect) and masculine characteristics (androgenic effect). Prescription medicines in most countries and controlled substances in many.
Aromatization
The conversion of androgens such as testosterone into estrogens by the enzyme aromatase, mainly in fat tissue. Higher androgen levels mean more estrogen produced this way.
Calorie deficit
Consuming less energy than the body uses, so that stored fat (and, if the deficit is too large, muscle) is used to make up the difference. The basis of every fat-loss diet.
Estradiol (E2)
The main form of estrogen in the body. In men it is produced mostly by aromatisation of testosterone and is needed in a narrow range for bone, cardiovascular and sexual health.
Gynecomastia
Growth of breast gland tissue in men, caused by an imbalance between estrogen and androgen action. With anabolic steroids it results from estrogen produced by aromatisation.
Hematocrit
The percentage of blood volume made up of red blood cells. Anabolic steroids stimulate red cell production, and a hematocrit above the normal range thickens the blood and raises the risk of clots, stroke and heart attack.
HPG axis (hypothalamic-pituitary-gonadal axis)
The hormonal feedback loop that controls the body's own production of testosterone or estrogen. The hypothalamus releases GnRH, the pituitary releases LH and FSH, and the testes or ovaries respond by producing sex hormones.
Hypogonadism
A condition in which the testes or ovaries produce too little sex hormone. Anabolic steroid-induced hypogonadism (ASIH) is the persistent suppression of the body's own testosterone production after stopping anabolic steroids.
Post-cycle therapy (PCT)
The use of medicines after stopping anabolic steroids to help restart the body's own hormone production. Typically involves selective estrogen receptor modulators and sometimes hCG, prescribed and monitored by a physician.
SERM (selective estrogen receptor modulator)
A class of medicines, including clomiphene and tamoxifen, that block or activate estrogen receptors depending on the tissue. In the brain they block estrogen feedback, which raises LH and FSH and can restart the body's own testosterone production.
Testosterone replacement therapy (TRT)
Medically prescribed testosterone given to restore normal levels in men diagnosed with hypogonadism. Aims for physiological, not supraphysiological, levels and is monitored with regular blood tests.
Virilization
The development of masculine physical characteristics in a woman as a result of androgen exposure: deepening of the voice, facial and body hair, clitoral enlargement, breast tissue reduction and menstrual disruption.