Some researchers believe that decreased levels of the neurotransmitter serotonin lead to impotence. (32) Serotonin is a substrate of MAO. Ideally, MAO metabolises the serotonin so it will not become too prominent. Rising levels of MAO, which may appear after age 45 thus, accompany falling levels of serotonin. G.H.3 has a demonstrated ability to inhibit excess MAO. Thus it may tend to normalise serotonin levels and restore potency.

Estrogen and androgen production can be a factor in sexual characteristics and performance as well. Parhon, Aslan and Danila (33) and Untea (34) conducted studies in this area. They concluded that G.H.3 tends to increase deficient estrogen and androgen levels. It appears that this simulative effect only occurs where these factors are subnormal.