Testosterone can be administered parenterally , but it has more irregular prolonged absorption time and greater activity in muscle in enanthate , undecanoate , or cypionate ester form. These derivatives are hydrolyzed to release free testosterone at the site of injection; absorption rate (and thus injection schedule) varies among different esters, but medical injections are normally done anywhere between semi-weekly to once every 12 weeks. A more frequent schedule may be desirable in order to maintain a more constant level of hormone in the system.  Injectable steroids are typically administered into the muscle, not into the vein, to avoid sudden changes in the amount of the drug in the bloodstream. In addition, because estered testosterone is dissolved in oil, intravenous injection has the potential to cause a dangerous embolism (clot) in the bloodstream.
A derivative of Dihydrotestosterone (DHT) and sharing a similar chemical structure of the steroid epitiostanol, once ingested, epistane binds to the receptors of the body that are responsible for building lean muscle mass. It is a readily orally active compound, meaning it is best in capsule form for oral administration over injection. Once ingested epistane works by increasing the level of activity in the cells in androgen receptors, upon binding to these receptors, epistane signals for an increased retention of nitrogen within that cell as well as an increased level of protein synthesis, leading to an increased performance as the muscles can perform/recover/grow better.