Could be brain-specific too (sorry
). Seriously I was reading about this because it's been happening to me as well, and I don't think it's the medications. I'm been zeroing in on the hypothalamus lately...
The hypothalamus is a conglomerate of different nuclei (groups of neurons or brain cells), that sits just above the brainstem. It is responsible for many of the body's homeostatic mechanisms, from heat regulation, endocrine hormone production, and what we will discuss, hunger.
Hunger regulation takes place in one sub set of nuclei, called the lateral hypothalamus and the ventromedial hypothalamus, which controls satiety.
Simple take away: The LH controls hunger, if it is broke you won’t be hungry. The VMH controls satiety, if this is broke you never feel full.
LH neurons fire from some different stimuli such as seeing food, smelling food, and decreasing blood glucose and the signals are suppressed by eating.
This^ is from the hypothalamus section of
http://www.thewhitecoatfitness.com/hunger-signals-broke/
Another good article on the physiology of appetite:
http://www.montereydiet.com/ghrelin_and_leptin.html
Finally because there's so many possible influences, the
wiki page provides a good overview.