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. 
Testosterone, an essential precursor of estrogen in women, is made in the ovaries and adrenal glands. There is a steady decline in testosterone levels from the 20s through menopause. With surgical menopause, the level of testosterone drops precipitously. No clear lower limit of testosterone has been established; however 15 ng per dL ( nmol per L) commonly is used. One study 38 found that women with 0 to 10 ng per dL (0 to nmol per L) had markedly decreased sexual desire in all situations and absent or markedly decreased orgasms. Because of studies like this, supplemented with anecdotal evidence, many women have been started on testosterone therapy.