Scientists differentiate male steroids as being either primarily androgenic, which means that their predominant therapeutic use is to instill male gender characteristics or anabolic, for use of tissue growth and repair such as wound healing after an operation, building up red blood cell counts, or accelerating muscle growth and recuperation. 

Although the classic textbook definition of an anabolic steroid is being 'a synthetic derivative of testosterone', this is not perfectly true. There is a small group of anabolic steroids which are derivatives of estrogen and there also happens to be an anabolic steroid which is a progesterone (another female hormone) derivative.

But primarily, scientists have analyzed the testosterone molecule and have created steroids with a resemblance to it, but do have differences which can either make the new steroid either more androgenic, or more anabolic, or less androgenic. Some steroids have been designed to be both more androgenic and more anabolic at the same time.

Many athletes use powerful androgenic steroids, thinking that they are anabolic steroids, and use these particular ones because they do a better job anabolically than the so called anabolics. This must be confusing to many of you reading this, but it just illustrates that the whole steroid controversy is not so simple. 

In fact anabolic steroids have mistakenly gotten a bad reputation of having harmful side effects, but the truth is that it is mostly androgenic steroids with the bad side effects. If I seem to be overly picky on this point, I assure you that later on I will illustrate that this identity problem becomes more serious than mere semantics. 

If your view on anabolic steroids has become a little unfocused, I'm afraid that I will have to disorient you a bit more. An athlete can take what is known to be a predominantly anabolic steroid in such large amounts, that the cumulative dosage of the androgenic content of the steroid (which on a milligram per milligram basis is less than that of testosterone) makes his metabolism have a higher androgen content than what his own body would naturally produce while not using steroids.

Simply put: anabolic steroids will act as androgenic steroids if taken in large enough dosages. This is important to know because, many of the undesirable and harmful side effects that both men and women using steroids experience result from excess androgen.

Source:
Duchaine Daniel, Underground Steroid Handbook II, 2006
Hart Mick, Laymans Guides to Steroids
Hart Mick, Laymans Guides II - Return of the Syringe
Hart Mick, Laymans Guides III - Return of the Syringe
Hardcore, Complete Steroid Handbook, 2004