As Testosterone Propionate is, of course, Testosterone, it suffers from moderate aromatization which results in the Estrogenic side effects of bloating, water retention, elevated blood pressure (as a result of the bloating), and risks of gynecomastia. This soft and puffy look that bloating brings to the physique is generally undesirable for most users that wish to engage in cutting cycles or lean mass cycles. Therefore, Testosterone Propionate must be utilized with an aromatase inhibitor in order to disable the aromatase enzyme and eliminate the water retention effect of the Estrogen conversion, which should result in a harder looking physique without the soft puffiness. In doing so, Testosterone can successfully be utilized as a ‘hardening’ and cutting compound, as well as for lean mass gains. Some individuals prefer the water retention, convinced that it aids in protecting tissues and connective tissue from the stressors of heavy strength gains and heavy lifting, and therefore Testosterone is preferred as a bulking and strength gaining compound in this case. In any case, Testosterone is also an excellent compound for all-out bulking and strength gaining cycles, which is what its main use seems to be among bodybuilders and athletes. It is a very versatile compound that can provide the anabolic strength necessary for bulking phases.
The effects of testosterone in humans and other vertebrates occur by way of two main mechanisms: by activation of the androgen receptor (directly or as DHT), and by conversion to estradiol and activation of certain estrogen receptors. Free testosterone (T) is transported into the cytoplasm of target tissue cells, where it can bind to the androgen receptor, or can be reduced to 5α-dihydrotestosterone (DHT) by the cytoplasmic enzyme 5α-reductase. DHT binds to the same androgen receptor even more strongly than T, so that its androgenic potency is about times that of T. The T-receptor or DHT-receptor complex undergoes a structural change that allows it to move into the cell nucleus and bind directly to specific nucleotide sequences of the chromosomal DNA. The areas of binding are called hormone response elements (HREs), and influence transcriptional activity of certain genes, producing the androgen effects.