Sustanon is an oil-based injectable testosterone blend. It typically contains four different testosterone esters: Testosterone propionate (30 mg); testosterone phenylpropionate (60 mg); testosterone isocaproate (60mg); and testosterone decanoate (100 mg). Sustanon is designed to provide a fast yet extended release of Testosterone. The propionate and phenylpropionate esters are quickly utilized, releasing into circulation within the first four days. The remaining esters are much slower to release. Sustanon stays active in the body for about two and three weeks (respectively).

Sustanon was developed by Organon as an ideal HRT (Hormone Replacement Therapy) solution, and it was thought at the time that the different esters would be able to provide a constant release of Testosterone over a months time.

The advantage to this drug, according to the manufacturer, is that it can be injected once a month, and the different esters would provide different timed releases over that month, and the patient would therefore only need to visit the doctor once a month for his shot.