Tibolone has tissue -selective estrogenic effects, with desirable effects in bone , the brain , and the vagina , and lack of undesirable action in the endometrium and breasts .  Its tissue selectivity is the result of metabolism , enzyme modulation (., of estrogen sulfatase and estrogen sulfotransferase ), and receptor modulation that vary in different target tissues, and differs mechanistically from that of selective estrogen receptor modulators (SERMs) such as tamoxifen , which produce their tissue selectivity via means of modulation of the ER.   As such, to distinguish it from SERMs, tibolone has been described as a "selective tissue estrogenic activity regulator" (STEAR),  and also as a "selective estrogen enzyme modulator" (SEEM). 
The Phenylpropionate ester is a moderately small or short ester, possessing a half-life far shorter than longer esters such as Enanthate or Cypionate but larger and longer than esters such as Propionate. To give a point of reference, Nandrolone-Decanoate will carry with it a half-life of approximately fifteen days while the Phenylpropionate form of nandrolone will only possess a half-life of approximately 96-120 hours. For this reason, steroids with the Phenylpropionate ester attached will need to be administered more frequently than longer ester based steroids such as Decanoate or Enanthate. Most Durabolin users, as this is the most common Phenylpropionate based steroid will find injections every three days to be the minimal time frame while every 48 hours will prove to be far more efficient.
Heavy consumption of the essential amino acid lysine (as indicated in the treatment of cold sores) has allegedly shown false positives in some and was cited by American shotputter C. J. Hunter as the reason for his positive test, though in 2004 he admitted to a federal grand jury that he had injected nandrolone.  A possible cause of incorrect urine test results is the presence of metabolites from other AAS, though modern urinalysis can usually determine the exact AAS used by analyzing the ratio of the two remaining nandrolone metabolites. As a result of the numerous overturned verdicts, the testing procedure was reviewed by UK Sport . On October 5, 2007, three-time Olympic gold medalist for track and field Marion Jones admitted to use of the drug, and was sentenced to six months in jail for lying to a federal grand jury in 2000.