Testicular atrophy is often caused by steroids usage. So discontinuing them helps in a lot of cases. In other cases doctors recommended a prescribed dosage of testosterone which is effective in regaining the original size. However, taking testosterone over a long time can actually have the opposite effect so you have to stay in touch with your physician and not take them for too long a period. In some cases doctors rely on the HCG treatment which is quite effective in case of testicular atrophy. However, it is also closely linked to testicular tumors so before you go on to take any medicines do rule out that possibility by getting yourself examined. Good luck!