Shelton and Rajfer (2012) noted that androgen deficiency in aging men is common, and the potential sequelae are numerous. In addition to low libido, erectile dysfunction, decreased bone density, depressed mood, and decline in cognition, studies suggest strong correlations between low testosterone, obesity, and the metabolic syndrome. Because causation and its directionality remain uncertain, the functional and cardiovascular risks associated with androgen deficiency have led to intense investigation of testosterone replacement therapy in older men. Although promising, evidence for definitive benefit or detriment is not conclusive, and treatment of LOH is complicated.
The mean oral bioavailability of finasteride is approximately 65%.  Its volume of distribution is 76 L/kg.  The plasma protein binding of finasteride is 90%.  The drug has been found to cross the blood–brain barrier , whereas levels in semen were found to be undetectable.  Finasteride is extensively metabolized in the liver , first by hydroxylation via CYP3A4 and then by aldehyde dehydrogenase .  The metabolites of finasteride have about 20% of its potency in inhibiting 5α-reductase and hence its metabolites are not particularly active.  The drug has a terminal half-life of 5 to 6 hours in adult men (18–60 years of age) and a terminal half-life of 8 hours or more in elderly men (greater than 70 years of age).  It is eliminated as its metabolites 57% in the feces and 40% in the urine . 
DHT is a potent agonist of the AR, and is in fact the most potent known endogenous ligand of the receptor. It has an affinity (K d ) of to nM for the human AR, which is about 2- to 3-fold higher than that of testosterone (K d = to nM)  and 15–30 times higher than that of adrenal androgens .  In addition, the dissociation rate of DHT from the AR is 5-fold slower than that of testosterone.  The EC 50 of DHT for activation of the AR is nM, which is about 5-fold stronger than that of testosterone (EC 50 = nM).  In bioassays , DHT has been found to be - to 10-fold more potent than testosterone.