A study done by The Harvard School of Public Health reported that Americans with mental illness are nearly twice as likely to smoke cigarettes as people with no mental illness. People with diagnosable mental illness comprise nearly 45% of the total tobacco market in the United States. Nearly 1/3 of smokers with mental illness were able to quit smoking. If they refrained from using alcohol and drugs, they had a cessation rate equal to people without mental illness.
Mental illness in this instance was defined as one of the following: major depression, bipolar disorder, agoraphobia, social and simple phobia, generalized anxiety disorder, alcohol abuse and dependence, antisocial personality, conduct disorder, non-affective psychosis (including schizophrenia). So you can see the people in the study were at varying degrees of severity in their illness.
I know that for many years doctors did not pressure me to quit smoking. I was more concerned about my smoking than they seemed to be, until it started impacting other areas of my (physical) health. It was only this year that I met a physician (internist) who understood that I was self-medicating my depression with nicotine, and maybe he only understood because I was talking to him as a recovering nicotine addict rather than as a smoker. I had some perspective about my smoking. But I also know that when I was hospitalized, the patients smoked up a storm and nobody tried to stop them. The attitude in many cases is that smoking is a stress buster. The people here on the EX site know that's a lie.
If you want to read about the study, here is a link to an article:
But if you suffer from any of these disorders, do not think that quitting is impossible. I will have 3 years without nicotine on November 11th. Stick with the quit.