[Smoking and schizophrenia: where is the biological connection?].

Objective: Patients with psychiatric disorders have a higher incidence of smoking than the general population. In particular, the rate of smoking among patients with schizophrenia has been found to be between two and three times in the general population in western countries. This paper reviews the biological factors that might be contributing to the high rate of smoking among patients with schizophrenia and examines the interaction between nicotine and neurobiological disturbances observed in schizophrenia.

Method: Papers assessing the possible biological causes of smoking in patients with schizophrenia and the physiological effects of nicotine were reviewed by using the key words "nicotine, schizophrenia, smoking and cigarette" in Pubmed, Turk Medline, and the Turkish Psychiatric Index.

Results: Studies conducted in humans and animals show that nicotine can directly increase dopaminergic transmission in the central nervous system, enhance cognitive performance and improve sensory gating deficits observed in patients with schizophrenia. Moreover, smoking diminishes the efficacy of most antipsychotic drugs via an increased hepatic metabolism.

Conclusion: Studies suggest a link between the physiological effects of nicotine and the neurobiological disturbances in schizophrenia. Disturbances in the cholinergic transmission may be responsible for some symptoms of schizophrenia. The harmful effects of smoking vastly outweigh any possible benefits, but, nevertheless, further investigation may lead to important insights regarding the etiology of schizophrenia at a molecular level.