some medical students have analysed Gollum's mental state
He shows no evidence of any cognitive impairment. He has poor insight into his condition but he is aware of the Gollum-Sméagol dissociation. [...] On initial consideration schizophrenia seems a reasonable diagnosis. However, in the context of the culture at the time it is unlikely. Delusions are false, unshakeable beliefs, not in keeping with the patient's culture. In Middle Earth, the power of the ring is a reality.
Be sure to check out the comments at the end of the article too by the way. Funny stuff:
However, given the poor quality of Gollum's diet, he needs to see a dietitian in addition to a pyschiatrist.
Via: Librarian in Black.