Steroids are chemical derivatives of cholesterol.
Despite a recent bad press, it is in fact an essential cellular component in mammals (the average human adult carries about 250g) and undergoes further biosynthetic transformations which leads to the sex hormones testosterone & oestradiol.Anaboic steroids, when invented were based on three structural changes to the testosterone molecule:
1) esterification of the 17 beta-hydroxyl group to retard the rate of drug metabolism (enanthate, decanoate, cypionate, and phenylpropionate forms);
2) alkylation of the 17 alpha position to allow for oral administration (methyl testosterone); and
3) alterations of the testosterone ring structure including parenteral forms such as nandrolone (Durabolin®, Deca-Durabolin®) and methenolone enanthate (Pimobolin®), and oral derivatives such as oxandrolone (Anovar®) and methandostrostenolone (Dianabol®).
Some resulting drugs, particularly those involving 17 alpha alkylation, are more likely to affect liver function and produce cholestatic hepatitis and tumors with long-term use.
Strickland, A.L. "Steroids: Do They Enhance Athletic Performance?" The Journal of the South Carolina Medical Association. February 1988. Describes general characteristics of steroids, which include a variety of compounds of different classes and entirely different effects, differentiated primarily by the number of carbon atoms in the nucleus.
All anabolic steroids in use today are variations of one of those three changes to the testosterone molecule. These chemical classes of anabolics are taken by different routes and have different side effects on the body. The 17-alpha-alkylates and 1-methyl compounds are taken by mouth, while 17-beta-esters must be injected to be effective.