Schizophrenics also self-medicate with nicotine. 80% of schizophrenics are smokers and they smoke 3 times more than typical smokers. (https://brainblogger.com/2009/07/03/why-do-schizophrenics-smoke-cigarettes/)

Nicotine seems to dampen the "volume" of auditory halluncinations as well as increasing their ability to focus.