Silent Night, Bloody Night (1972) - very classic retro horror slasher flick--takes place in a mansion that is a former asylum which a man has inherited and goes to investigate with his wife on Christmas Eve. I saw this when I was little, but I don't remember it well so I may watch later. Bookmark! It takes place in sort of a fake Salem, Massachusetts "esque" town.
Braniac (2004) - Brain chemistry research produced a drug called Nirvana that wipes out addiction and mental illness by stimulating pleasure centers in the brain and flooding the brain with endorphins. PsyMax Labs is about to release Nirvana, but suddenly things go awry. The drug causes drastic genetic changes, switching on dormant genes to produce BRAINIAC, a creature whose need for the brain's pleasure chemicals causes it to begin eating human brains.
Scared Stiff Reviews reviewed the film and you can read their review here!
Holy crap! Is he going poop? Or she, excuse me, maybe the monster that lives inside this guy is a girl.
The Abomination (1986) -A young man goes on a killing spree to feed a monster living inside him.
This looks promising. I have not seen this flick or Braniac. I will be watching them soon and I will let you know or feel free to ask me on Facebook or comment below in the comment box if you feel the inclination.