The body produces testosterone naturally, but natural
testosterone cannot be used as a medicine. In the normal body,
testosterone is released continuously into the bloodstream by the
pituitary gland. In males, it is also released by the testes. It
reaches different parts of the body, has its effects, and then body
enzymes quickly break it down.

When males reach the end of puberty, the amount of
testosterone rises suddenly and stays at a high level for four to
six months before returning to normal. During this time, the
growth plates in the long bones of the arms and legs close, the
voice deepens, facial hair begins to grow and the male sex organs
grow in size. It is this surge in testosterone that completes the
sexual maturation of males.

Some males do not experience this burst of testosterone. When
the role of testosterone was discovered, medical researchers tried
to treat delayed puberty by giving them testosterone. They
discovered that a single dose of testosterone, even a very large
one, is so rapidly broken down by body enzymes that it cannot
imitate the natural hormone surge. To use natural testosterone for
this purpose, a boy would have to have an intravenous infusion bag
constantly putting testosterone into his veins day and night for at
least four months!

The researchers needed to find a way to prevent the body from
breaking down the testosterone so quickly. Through trial and
error, chemists discovered how to alter the testosterone molecule
so it would last longer.(1,2)

There are many kinds of anabolic steroids available to treat
several disease states. In the past, anabolic steroids were taken
from animal tissues for use in early experiments.(1) Today,
anabolic steroids are chemically manufactured rather than being
purified from natural sources.