I would imagine that over treatment, or illness where med’s have been doubled or tripled could cause loss of libido.  If his doses where too high, I would imagine testoserone levels and dhea levels are low.  Does he have regular blood tests and when was the last one?  Did they check for the male androgen levels to make sure his levels were ok?  

Many men and women (non-cah) lose interest in sex when they are depressed or stressed and this is generally when the cortisol levels are at their highest, so it stomps on the testosterone levels and dhea levels a little.  That is why I suggest that, because if the doses of cortisol are too high, this could cause that to happen I feel.  Has he had any other symptoms such as depression or does he ever get over emotional?   From what I can gather men have less tendency to talk about their feelings than women and are much less likely to admit they are depressed or feeling down.  Perhaps he needs to go chat to his Doctor about the libido because I am quite sure they can check things over for him and do a few blood tests to rule these things out and then look at what can be done.

Regards

Anne-Marie