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. 
The findings suggest that testosterone treatment plays an important role in female-to-male transitions, by enabling patients to not only look more masculine, but also think in a more masculine manner. Hormones are regulatory substances produced by the body to help stimulate specific body functions. Among its many uses , the sex hormone testosterone is often given to transgender men in an effort to help their body take on more masculine features. The most obvious effects of testosterone treatment are those that can be easily observed , such as a deeper voice, increased body hair, rearrangement of body fat distribution, and an increase in acne. However, testosterone also causes subtle but equally significant body changes. For example, testosterone treatment can also cause psychological changes , such as mood swings, anxiety, and agitation.
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