For use in bodybuilding, testosterone is almost always used as an injectable ester or suspension due to poor oral bioavailability and the impracticality of high dose transdermal or sublingual delivery. All testosterone forms in a wide sense are the same: active agent testosterone + ester attached, which determines release time and duration of the compounds active life. In a nutshell: long esters release the active agent into the blood slowly, but provide a stable hormone level for a long time (depending on the ester), without creating peaks.
It shall be noticed, that in men, approximately 5% of testosterone undergoes 5α-reduction to form the more potent androgen, dihydrotestosterone (DHT), also known as androstanolone. From another side approximately 0.3% of testosterone is converted into estradiol (the primary female sex hormone) by aromatase an enzyme expressed in the brain, liver, and adipose tissues. Hence, don`t forget to take precautions to avoid respective side effects. Thereof we recommend to perform blood works and take aromatase inhibitors on cycle (if required, anastrozole preferably) and SERMs (clomifene, toremifene) during post cycle therapy (PCT).