Libido

Libido in men (and women) is driven by testosterone. Desire disorders 
may present as hypoactive desire disorder (often lifelong), inhibited 
desire (may be situational) and desire discrepancy (an increasingly 
common disorder in couples)
Desire problems in younger men mostly have a psychological basis 
(often around commitment issues). Older men experience a slow 
decline in testosterone levels at about one per cent a year from 
the age of 40. This may not only reduce libido but may also result 
in a controversial condition called partial androgen defciency in the 
ageing male (PADAM). As men age, higher levels of sex hormone 
binding globulin reduce the amount of bioavailable testosterone. 
The clinical symptoms of PADAM are said to be deceased libido, 
ED, depression, fatigue, decreased muscle mass, decreased bone 
density and increased visceral fat. Yet men who are depressed  
may be accused of having PADAM due to the similarity of  
presenting symptoms.
Testosterone is a requirement for nocturnal erections but appears 
to play only a minor role in the quality of sexually induced erections. 
Testosterone, through its receptor sites in cavernosal tissue, helps 
improve the action of PDE5 inhibitors which otherwise have poor 
results in hypogonadal men. Treatment with testosterone may 
increase libido and provides an improved sense of wellbeing. 
However, it may also aggravate prostate disorders, raise haematocrit 
and aggravate symptoms of sleep apnoea.