A Card Up the Sleeve
It doesn't take much of an imagination. Over the decades, amphetamines, anabolic steroids, erythropoietin, self-transfusions, and gonadotropins have been used to improve performance in the Olympics and other international competitions.
It's almost a given that the discovery of a new medical treatment will find its application in performance enhancement. Even investigational drugs such as Andarine (a selective androgen receptor mediator), GW1516 and Acadesine (AMPK activators) are available on the online black-market and could be used as anabolic steroids and endurance boosters, respectively.
While many of these drugs are relatively easy to detect, manifesting themselves as anomalous compounds or metabolites that can be detected via GC/MS or LC/MS, drugs that mimic naturally occurring molecules such as erythropoietin (EPO) or human growth hormone (hGH) prove to be a little more difficult.
ELISAs to detect pharmaceutical formulations of the molecules are one option. PEGylation and domain being are the major structural differences for EPO varieties. But hGH is a more difficult challenge, and detecting administered hGH may rely on the ratio of its naturally occurring isoforms or other protein levels that may be affected by a sudden dose.