Most anabolic steroids act by activation of androgen receptors. Results of androgen receptor activation are traditionally divided into anabolic and virilizing effects.

Examples of anabolic effects:
  - Increased amino acid incorporation into protein synthesis 
  - Increased muscle mass and strength 
  - Increased appetite
  - Increased bone remodeling and growth

Examples of virilizing effects:
  - Increased growth of androgen-sensitive hair (beard, chest, limbs) 
  - Increased vocal cord size, deepening the voice 
  - Increased libido 
  - Suppression of endogenous sex hormones 
  - Impaired spermatogenesis

Many androgens are metabolized to compounds that also cross-react with estrogen receptors, producing an additional set of (usually) unwanted effects:
  - Accelerated bone maturation (in children) 
  - Increased breast growth (in males) 

A hormone with purely anabolic effects would have many uses, but in many cases the usefulness is limited by unwanted virilizing effects. Many of the synthetic anabolic steroids were produced in an attempt to find molecules that produced a higher degree of anabolic rather than virilizing effects.

From Wikipedia, the free encyclopedia