Sustanon 250 by Balkan Pharmaceuticals (or similar brands) is a 250 mg/mL injectable testosterone blend composed of four esters—propionate, phenylpropionate, isocaproate, and decanoate—designed to provide both rapid and sustained testosterone release after intramuscular injection . It is used medically for testosterone replacement therapy in men with hypogonadism and sometimes in gender‑affirming treatment in trans‑masculine individuals but is not FDA‑approved in the U.S. . Users typically inject every 2–3 weeks—though more frequent dosing (e.g. every other day) may be recommended to avoid hormone fluctuations from the short esters . Common effects include increased muscle mass, libido, and energy, but side effects may encompass acne, oily skin, fluid retention, mood swings or aggression, elevated blood pressure, polycythemia, and potential suppression of natural testosterone leading to infertility or testicular atrophy . In women or children, virilization effects such as voice deepening, increased body hair, and growth acceleration are possible; thus, it’s contraindicated during pregnancy and for those with peanut or soy allergies (it’s suspended in peanut oil) .