A cross-sectional study of 131 patients with schizophrenia found that patients with mild-moderate dependence exhibited greater scores on the Positive and Negative Syndrome Scale (indicating how ill the patient was), and smokers with mild nicotine dependence had comparatively greater negative symptoms than nonsmokers with schizophrenia. 

Arguments Against the Self-Medicative Hypothesis

Those with psychiatric disorders comprise 44% of cigarette sales in the United States. Since the 1950s, researchers funded by the tobacco industry have been studying the connection between psychiatric illnesses and smoking. The self-medication theory was proposed in the 1980s by a tobacco-industry-affiliated researcher who claimed that nicotine may help people with schizophrenia in a “therapeutic” way. Some non-industry-affiliated researchers have contended that this self-medication hypothesis has promoted smoking to a vulnerable audience with psychiatric conditions. 

Connection Between Self-Medicative Hypothesis and the Tobacco Industry


The self-medicative theory suggests that smokers with schizophrenia try to alleviate their negative symptoms through nicotine – a substance which increases dopamine and glutamate levels in the prefrontal cortex. This would counteract the ways schizophrenia would neurologically affect these smokers. 

University of Michigan - Ann Arbor

The smoking prevalence in schizophrenia is at 70-80%, with the prevalence of cigarette smoking at initial onset of psychosis being at an estimated 58% of studied patients. Smokers with schizophrenia tend to inhale deeper, smoke for longer durations, consume higher amounts of cigarettes, and have higher nicotine dependence compared to smokers without schizophrenia. There are competing theories as to why this high association between smoking and schizophrenia exists. 

The High Association Between Smoking and Schizophrenia

Ding JB, Hu K. Cigarette Smoking and Schizophrenia: Etiology, Clinical, Pharmacological, and Treatment Implications. Schizophr Res Treatment. 2021 Dec 13;2021:7698030. doi: 10.1155/2021/7698030. PMID: 34938579; PMCID: PMC8687814.



Cigarette Smoking and Schizophrenia: Etiology, Clinical, Pharmacological, and Treatment Implications


Self-Medicative Hypothesis

Several academic studies have corroborated the theory that there is a potential causal relationship between smoking and schizophrenia.

Causative Theory of Smoking and Schizophrenia


A third theory as to the link between smoking and schizophrenia suggests that there are common genetic risk factors for nicotine dependence and schizophrenia. However, in a Swedish study comparing pairs of identical twins, full sisters, half sisters, and female cousins, the research team found that there was no significant decline in hazard ratio for developing schizophrenia across relatives with less genetic relationship. When looking at the identical twin pairs, it was found that the twin who was a heavy tobacco smoker was 1.7 times more likely to develop psychosis compared to her non-smoking twin. This therefore suggests there is not strong evidence for the “common genetic risk factors” theory. 

Common Genetic Risk Factors Theory

Previous studies on tobacco smoking have suggested that nicotine might alter dopaminergic, cholinergic, and glutamatergic neurotransmitter signals. Studies of adolescent nicotine exposure show that tobacco smoking may potentially influence brain development — or even restructure the brain in terms of a decrease in gray matter in the prefrontal cortex — with adolescents who use inhalants having an increased risk of having psychotic disorders, strengthened negative emotions, and alterations in cognitive functioning. This is concerning, given the increasing usage of e-cigarettes among the adolescent population. 


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