It's been found that many people suffering from schizophrenia experience a reduction in the negative symptoms of the disease (hallucinations, delusions) when they are smoking and an increase in these symptoms when they cease smoking. It is inferred, therefore, among some practitioners, that smoking is itself a form of self-medicating which people with schizophrenia naturally gravitate toward.
The problem, of course, is that smoking is just as much of a health hazard for those suffering with mental illness as it is for anyone else in the general population. The increase ofasthma, emphysema, lung and mouth cancer, as well as heart diseasecompounds the mental, emotional and physical struggles that people with schizophrenia are already facing. The medical costs of smoking are tremendous, as well, not to mention the cost of cigarettes themselves.
https://www.empowher.com/schizophrenia/content/nicotine-addiction-and-schizophrenia