Breast tenderness and gynecomastia can occur when it is taken in high dose. In high doses, it can change the mood, increase sex drive, aggression, nocturnal emissions and spontaneous erections.  There are other effects like increases the red blood cell ratio to total volume ( hematocrit ) and worsening of sleep apnea. More serious of the side effects includes liver toxicity and heart disease.  Sustanon Alternative Sustanon is a great steroid that is hampered by side effects. It can be potentially harmful to the body with some effects yet to be discovered. It is not intended for performance enhancement for bodybuilders because it is mostly used for therapeutic functions.