Several mechanisms are believed to underlie the phenomenon of nicotine addiction and mental-health disorders as comorbidities. One is the ability of nicotine to reduce the severity of some psychiatric symptoms. For example, the release of serotonin and norepinephrine in the brain by nicotine is similar to the neurochemical effects of some antidepressant medications. Nicotine may improve sensory gating (the process by which the brain responds to stimuli), which is abnormal in schizophrenics. Improvement in sensory gating secondary to nicotine intake might be expected to enhance the ability to sort out extraneous stimuli and therefore improve attention (Martin and Freedman, 2007). In addition, cigarette smoking inhibits monoamine oxidase A and B (Lewis et al., 2007); such inhibition is used to treat depression, therefore cigarette smoking might benefit depressed patients in the same manner. Finally, nicotine, through its stimulant effects, may reduce unpleasant sedative side effects of psychiatric medications and reduce the sedation caused by alcohol.
There is a substantial link and possible shared genetic susceptibility between alcohol abuse and cigarette smoking (Le et al., 2006; Madden and Heath, 2002; Wilhelmsen et al., 2005). The 2001–2002 NESARC found the 12-month prevalence of nicotine dependence to be 45.4% in people who were alcohol-dependent (Grant et al., 2004). Alcohol abusers are more likely to die from smoking-related causes than from alcohol (Burling and Ziff, 1988; Hurt et al., 1996). In a study of 499 smokers who were receiving intensive treatment for alcohol dependence, 95% considered themselves to be physically addicted to nicotine, and they smoked a mean of 25.5 cigarettes/day. Over 45% of the participants lived with another smoker, 39% had attempted to quit in the preceding year, 46% indicated that they were taking action to quit, and 33% were starting to think about quitting. 16.7% thought they should quit but were not ready. Only 8% had been told by an alcohol counselor to quit smoking and alcohol concurrently, 32% had been counseled to quit smoking in the future, and 24% had been advised to not quit by their alcohol counselor (Joseph et al., 2003). In a review of 24 smoking-cessation studies of people in treatment for substance abuse or dependence, Sussman (2002) found that quit rates increased with length of abstinence from substance use. Although some substance abusers may not benefit from or may even be harmed by concurrent treatment, for most “attempting to quit smoking does not seem to interfere with recovery from other substances … and concurrent exposure to smoking cessation treatment will assist with recovery.” Sussman noted that substance users who smoke differ from nonusers who smoke in several