This paper examines the elevated rates of tobacco use among individuals diagnosed with schizophrenia and bipolar disorder compared to the general population. Drawing on peer-reviewed literature, it reviews epidemiological findings, genetic associations — particularly the NR4A3 gene polymorphism — and the self-medication hypothesis as explanations for high smoking prevalence in these populations. The paper also considers the role of nicotine in cognitive function and mood regulation, identifies key gaps in the current literature, and proposes directions for future research and policy. A personal commentary reflects on the tobacco industry's potential role in reinforcing smoking behavior among people with severe mental illness.
The paper demonstrates effective synthesis of multiple peer-reviewed sources around a single explanatory framework — the self-medication hypothesis — testing it against genetic, epidemiological, and cognitive evidence. Rather than summarizing each study in isolation, the writer consistently returns to the central question of why smoking rates are elevated in these populations, using each source to either support, complicate, or qualify the hypothesis.
The paper opens with an introduction that establishes prevalence and the core comorbidity claim. A background section defines the disorders and key terms. The central literature review section presents findings in thematic order: epidemiological studies, smoking rates by disorder, genetic factors, and cognitive effects. A future implications section identifies research gaps, followed by a reflective personal commentary. The paper closes with APA-formatted references.
Schizophrenia and bipolar disorder are common mental disorders that reduce the lifespan of affected individuals relative to the general population. Substance use disorder is a frequent comorbidity in these individuals. Supporting data from several studies show that smoking rates among people with schizophrenia and bipolar disorder are two to three times those of the general population. It is hypothesized that this is because these individuals perceive smoking as reducing the severity of their symptoms and improving their quality of life, though this has not been confirmed through research.
Findings from current literature also suggest that smoking among people with schizophrenia and bipolar disorder may be related to the NR4A3 gene, which has several polymorphisms. By reviewing current research findings from peer-reviewed journals, this paper identifies gaps in the literature, describes implications for future research, and offers a personal commentary on the topic.
Schizophrenia is a chronic mental illness affecting approximately 1% of the world's population. According to the World Health Organization (WHO), it is more common among younger people between the ages of 20 and 45 than in older age groups. The WHO categorizes schizophrenia as one of seven diseases that disable people in this age range — ranking it above HIV, diabetes, and cardiovascular disease (Leucht, Burkard, Henderson, Maj, & Sartorius, 2007).
As a result of the disorder, individuals become unable to distinguish reality from fantasy, which impairs their ability to make clear and well-directed decisions and to respond normally in emotional situations (Johnson et al., 2010). They also become unable to behave appropriately in social contexts. Suicide is a well-documented feature of schizophrenia. Multiple reviews have identified excess mortality in schizophrenics at roughly twice the rate of the general population, suggesting that schizophrenia is a life-shortening disease (Kotov, Guey, Bromet, & Schwartz, 2010).
Bipolar disorder is a mental illness characterized by alternating episodes of extreme elation and depression, including severe mood swings. It affects men and women equally and is most common in younger individuals between the ages of 15 and 25, though it can also occur in older adults. Symptoms include poor judgment, emotional volatility, reckless behavior, lack of self-control, elevated mood, hyperactivity, high self-esteem, increased energy, and easy agitation.
Comorbidity refers to the presence of two or more diseases or disorders in an individual at the same time. These conditions may occur dependently or independently. Comorbidity of mental disorders alongside substance use disorders is extremely common and is typically associated with poor treatment outcomes and a more severe illness course. This makes it very difficult to identify, prevent, and manage comorbid disorders, which has prompted growing interest from researchers and policy makers seeking to understand how to deliver services that reduce comorbidities at both the individual and community level.
From an epidemiological standpoint, an "ever smoker" is someone who has smoked more than 100 cigarettes in their lifetime. Clinically, it refers to someone who has smoked daily for some period of their life. A "current smoker" epidemiologically is someone who smokes daily or on particular days; the clinical definition is narrower and limited to daily smokers. "Smoking cessation" epidemiologically means having ever smoked but not currently smoking, while clinically it refers to stopping daily smoking. This paper uses epidemiological definitions given their broader scope. Tobacco use is defined as the use of any tobacco product, including cigarettes, snuff, chewed tobacco, cigars, or pipes.
The U.S. Epidemiological Catchment Area (ECA) study, conducted on 20,000 respondents, was the first to establish comorbidity between mental disorders and drug abuse disorders. It found that the most significant drug-related disorder was tobacco use, and that comorbidity was highest in patients with personality disorders such as bipolar disorder and schizophrenia. A subsequent study in the early 1990s, the National Comorbidity Survey (NCS), examined the extent of comorbidity between severe mental illnesses and substance use and arrived at similar conclusions. These two studies gave rise to the hypothesis that patients with severe mental illnesses turn to substances such as tobacco to alleviate their symptoms. One theoretical basis for this is the "tension reduction" hypothesis proposed by Cappell and Greeley (1987), which argues that individuals with anxiety or personality disorders use substances like alcohol and tobacco to manage negative moods.
Smoking is particularly prevalent among people with schizophrenia. A review conducted across 20 countries found that approximately 62% of schizophrenics are also smokers, which led to the hypothesis that schizophrenia promotes smoking because nicotine helps reduce symptoms of the disease. This hypothesis is supported by studies conducted in Japan, the United Kingdom, Israel, and Russia that found higher rates of tuberculosis and other bacterial respiratory tract infections among schizophrenics compared to the general population. A study in Romania similarly suggested comorbidity between schizophrenia and tuberculosis, though researchers noted that the high national prevalence of tuberculosis may be a confounding factor. Other studies have pointed to impaired lung function among schizophrenics. Some researchers have also proposed that smoking may contribute to the development of schizophrenia through alterations in neurochemical systems, though no study has substantiated this claim. One additional study found that the association between schizophrenia and smoking may only hold in countries where tobacco is readily available.
Smoking has also been associated with other severe mental illnesses, including bipolar disorder and major depression, though relatively few studies have explored these relationships. One study reported that 69% of bipolar patients smoke daily, compared to 34% of patients with major depression and 23% of the general population. Another study placed the general population's daily smoking rate at 24%, compared to 64% among schizophrenics, 66% among bipolar patients, and 60% among those with major depression.
Bipolar patients are also associated with decreased smoking cessation and higher odds of becoming current or ever-daily smokers, suggesting increased initiation of smoking in this population. The same study found a higher risk of heavy smoking among bipolar patients. Confounding variables such as gender and genetic factors are thought to influence these results (de Leon, Gurpegui, & Diaz, 2007).
Two major reasons are given for elevated smoking rates among patients with severe mental illnesses. First, increased initiation — either by first-time smokers or relapsed former smokers. Second, reduced cessation. Both may be linked to the observation that patients with severe mental illnesses report better quality of life and reduced symptoms as smokers rather than as non-smokers. Nicotine has recognized antidepressant properties, and difficulties in cessation may be associated with the depression that accompanies severe mental illnesses (Graham, Frost-Pineda, & Gold, 2007).
Novak et al. (2010) investigated potential genetic factors that predispose patients with severe mental illness to tobacco use, motivated by the goal of identifying new targets for effective treatment. Their study focused on the NR4A gene, which has several polymorphisms potentially associated with increased smoking in individuals with severe mental disorders. The NR4A gene has also been linked to increased drug addiction more broadly. The researchers examined six single nucleotide polymorphisms (SNPs) and found that the NR4A3 allele is positively associated with the risk of smoking in bipolar patients. A similar association was found in the schizophrenic population. The study also found that these gene variants were significantly responsible for heavy smoking in the general population, with the variant appearing at lower frequency among mild smokers. This suggests that the allele is associated not only with the risk of smoking but also with its intensity. The NR4A3 gene is thought to modulate nicotine's effects in the brain, and this effect is believed to be stronger in individuals with severe mental illness, though this has not yet been confirmed by research.
Diaz et al. (2009) compared neurocognitive test performance between smokers and non-smokers among patients with severe mental illnesses. Their study was motivated by earlier findings showing that cigarette smoking and nicotine administration improve certain aspects of cognitive dysfunction in schizophrenic patients. While several studies have supported this finding, others have reported no effect or even a detriment to schizophrenic patients from tobacco use. More recent studies of non-psychiatric patients suggest that tobacco use degrades cognitive function, particularly in higher-order domains. Researchers also note that very little is known about the effect of smoking on the cognitive performance and symptom profiles of patients with severe mental illnesses. Diaz et al.'s findings indicated that improved cognitive function associated with smoking is present only in individuals with schizophrenia, and not in those with bipolar disorder or major depression.
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