Sustanon-250 is a mixture of testosterone esters, similar to the natural male hormone testosterone, in an oil solution. Testosterone is produced in the male gonads and Leydig cells and is the main endogenous hormone required for the development of the male reproductive organs (prostate, seminal vesicles, penis and scrotum) and secondary sexual characteristics in men (male-pattern hair development and distribution, laryngeal enlargement; change in tone of voice, body musculature and fat distribution).