Mind Over Mind — Karina Fabian

There are voices in Deryl's head.  They call him from consciousness, make him do odd things, overwhelm him with their needs. After five years in an asylum, he had a tenuous hold in his sanity, but no hope of a normal life--and he's only 18. Joshua, a talented but arrogant psychiatric intern, is hired to befriend Deryl.  Not content with a "buddy" role, Joshua uses neuro linguistic programming to help his troubled charge.  His methods work, but that's when the true danger begins.

Deryl's not crazy. He's psychic.

And the voices in his head are real.