How do anabolic steroids work?


A normal male produces 20 times more testosterone than a
normal female.(1) This extra testosterone is responsible
for greater muscle development in men than women, and the
development of other sex characteristics such as facial hair growth
and a deep voice.(2) Testosterone does these things when it
is absorbed from the bloodstream by certain types of
cells.(3) Molecules of testosterone fit themselves into
places inside the cells called "receptor sites," just as a key fits
into the lock designed for it. When the receptor site is filled by
the right type of molecule, it activates the cell to do specific
functions.(1) For example, in muscle cells, testosterone
promotes the production of protein.(3) There are only a
certain number of these "receptor sites" in each cell. If only a
few of them get filled by the right type of molecule, the cell will
respond at a low level. If all of them are filled, the cell gives
its maximum response.

A normal male secretes enough testosterone into his blood to
fill most of his testosterone receptor sites. However, if he takes
the huge doses of anabolic steroids that weightlifters take, the
cells will not be able to do any more than they would with a low
dose of steroids because the receptor sites are already filled
up.(3,4) The extra testosterone only makes side effects
more likely.