 CTA itself is inactive; it behaves as a prodrug to a weak estrogen that is formed as a metabolite via degradation of CTA in the liver.As such, the potency of CTA is reduced if it is given parenterally instead of orally.Although it is referred to as a weak estrogen and was used solely as an estrogen in clinical practice, CTA is a high-efficacy partial agonist of the estrogen receptor.