In an Israeli study of 14,248 military recruits without any prior history of major mental illness, it was found that over a 4-16 year period, participants who smoked over 10 cigarettes a day were 2.28 times more likely to develop schizophrenia compared to their peers. 



Israeli Study of Military Recruits


A Swedish study of 233,879 males and 1,413,849 females without history of psychosis found that there was a 3.45 hazard ratio for first-onset schizophrenia in heavily smoking females and a 3.80 hazard ratio for heavily smoking males, compared to a 2.21 hazard ratio for lightly smoking females and 2.15 hazard ratio for lightly smoking males. 

Swedish Population Study


Another study also found that prenatal exposure to smoke also increased the risk of developing schizophrenia by 29%. 

Study of Prenatal Exposure to Smoke

A meta-analysis of research regarding the relationship between smoking and schizophrenia found that 6 out of 8 studies indicated a statistically significant association between tobacco smoking and onset of schizophrenic symptoms. The strength of the associations ranged from a 50% increase to a 600% increase. Two of the studies indicated that smoking 10+ cigarettes a day was associated with a hazard ratio over 3. 

Meta-Analysis of Smoking-Schizophrenia Research

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

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


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. 

Self-Medicative Hypothesis

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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