Orexinergic neurons have been shown to be sensitive to inputs from Group III metabotropic glutamate receptors ,  cannabinoid receptor 1 and CB1–OX1 receptor heterodimers ,    adenosine A 1 receptors ,  muscarinic M 3 receptors ,  serotonin 5-HT 1A receptors ,  neuropeptide Y receptors,  cholecystokinin A receptors ,  and catecholamines ,   as well as to ghrelin , leptin , and glucose .  Orexinergic neurons themselves regulate release of acetylcholine ,   serotonin , and noradrenaline . 
In adults with GHD, the FDA-approved labeling states that the starting dosage of GH should be very low ( to mg/day). The product labeling further states that this dose should be increased gradually on the basis of clinical and biochemical responses assessed at monthly intervals. The biochemical marker generally relied upon for GH is the IGF-I level in serum. Values of IGF-I should be maintained in the normal age- and sex-adjusted range. The literature indicates that the dose may be increased, on the basis of individual patient requirements, to a maximum of mg daily in patients younger than 35 years of age, and to a maximum of mg daily in patients older than 35 years of age. Of note, this dose is substantially less than GH replacement doses in children and adolescents, in whom the dose is based on weight.
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 .