If you test out as deficient in testosterone, or if you have symptoms of low testosterone, you likely want to do something about it. There are definitely over-the-counter supplements designed for this very purpose. ( Alpha Male® and Tribex® are the most potent.) And while effective, they're best used by healthy younger men who want a boost in T levels for bodybuilding purposes. They probably aren't the best choice for men who are clinically low and who've made the choice to undergo what's usually a lifetime commitment to testosterone replacement therapy, or TRT.
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.