Different testosterone esters are often blended into one injectable preparation. In some cases up to seven esters are used, but the most popular formulation is that of Sustanon 250 where four esters are mixed together. This is done to take advantage of the faster acting esters while still only requiring weekly or bi-weekly injections. It is often believed to be a superior form of testosterone, but in reality it’s nothing more than just testosterone. One drawback of testosterone blends are that they incorporate esters with long carbon chains and those chains occupy allot of molecular weight, so the actual dosage of hormone is less than one would obtain from shorter esters like propionate. Testosterone blends are most useful during bulking phases where frequent injections are not possible.
Aromatase is an enzyme that converts testosterone into a form of estrogen called estradiol. Low levels of estrogen are important for bone density and cognitive and cardiovascular function. However, too much estrogen can cause unpleasant side effects such as loss of libido or sexual function and the development of breast tissue (gynecomastia) or tenderness of nipples. Aromatase is present in testis, liver, brain and fat tissue. The presence of aromatase in fat tissue can cause low T and high estrogen levels in overweight and obese men. Aromatase inhibitors (AIs) can reduce the amount of testosterone that is converted into estradiol. This can cause an increase in levels of LH, FSH and T and may consequently improve spermatogenesis. These medications are most effective treatment of low T or male infertility in obese patients or when the testosterone to estradiol ratio is less than ten.