Other significant adverse effects of testosterone supplementation include acceleration of pre-existing prostate cancer growth in individuals who have undergone androgen deprivation; increased hematocrit , which can require venipuncture in order to treat; and, exacerbation of sleep apnea .  Adverse effects may also include minor side-effects such as acne and oily skin, as well as, significant hair loss and/or thinning of the hair, which may be prevented with 5-alpha reductase inhibitors ordinarily used for the treatment of benign prostatic hyperplasia , such as finasteride .  Exogenous testosterone may also cause suppression of spermatogenesis , leading to, in some cases, infertility.  It is recommended that physicians screen for prostate cancer with a digital rectal exam and prostate-specific antigen (PSA) level before starting therapy, and monitor PSA and hematocrit levels closely during therapy. 
3) D Simon, MA Charles, K Nahoul, G Orssaud, J Kremski, V Hully, E Joubert, L Papoz, E Eschwege. Association between plasma total testosterone and cardiovascular risk factors in healthy adult men: The telecom study. Journal of Clinical Endocrinology and Metabolism 82:2(FEB 1997):682-685. Some doctors give the low dose injections of 25 mg of testosterone cypionate or enanthate every 2 weeks. The treatment for men who have almost no testosterone is 10 times that dosage. A normal male produces the equivalent of 100 mg of testosterone (enanthate) each week.