All progestins are not created equal.

Author: Stanczyk FZ.

Publication Year: 2003

Citation: Steroids 2003; 68:879-90.

This paper describes the molecular and pharmacokinetic differences between various progestins and progesterone.  Orally administered progestins require relatively high doses for therapeutic use because of extensive first pass metabolism in the liver.  Also, the various molecules show profound differences in progestational activity between human and animal tissues, particularly with respect to androgenicity, which has led to erroneous conclusions being drawn from animal studies regarding androgenicity in humans.  The author classifies the various molecules by chemical structure and concludes that they differ widely in metabolism, pharmacokinetics, and potency.

http://www.ncbi.nlm.nih.gov/pubmed/14667980