Mastabol is a synthetic derivative of dihydrotestosterone, displaying a potent androgenic effect that is responsible for increases in muscle density and hardness and a moderate anabolic effect that creates a positive nitrogen balance in humans and promotes protein synthesis. Since it is a derivative of dihydrotestosterone, dromastanolone does not aromatize at any dosage and thus it cannot be converted into estrogen. Therefore, estrogen-related water retention is eliminated. Mastabol 100 is relatively fast-actiing and fast-clearing because of the attachment of the propionate ester to the base molecule.