The numbers in the names refer to the fact that the content of testosterone compounds in each blend are 250 and 100 mg/ml, respectively.
The different testosterone esters provide for different half lives. Esterization of the testosterone molecules provides for a sustained (but non-linear) release of testosterone from the injection depot into the blood plasma.
While the intention of the mixed testosterone esters in Sustanon250 is to provide more stable serum testosterone levels, a single long-ester testosterone, such as testosterone cypionate or testosterone enanthate, may actually provide more stable serum testosterone levels.[medical citation needed]
This form of testosterone is a popular choice of anabolic steroid among bodybuilders and athletes.[