While there are multiple causes of testicular atrophy, the most common cause in resource rich settings is the use of anabolic steroids and their congeners in the treatment of male hypogonadism or testicular hypofunction.
It is perhaps the most dreaded side effect of Testosterone replacement therapy. While completely benign and reversible in most cases, it becomes an issue of cosmesis as well as reduced ejaculatory volume. The latter being due to the testes being a significant contributor to the ejaculatory fluid volume.
Testicular atrophy may be treated with Human Chorionic Gonadotropin (HCG), which is a peptide hormone usually obtained from the processing of the urine of pregnant women. You may have heard of it as Pregnyl® or Novarel®. It is a safe and well-tolerated injectable agent that can be safely and easily injected just under the skin.