Researchers have found that cigarette smoking may increase the risk of individuals to develop psychosis, particularly schizophrenia.

In the past, links between psychotic disorders and tobacco smoking have been recognized; however, the reasons supporting the associations are not clearly established. In this new study, researchers from the King's College London aim to test three of their hypotheses involved in the said correlation.

The first hypothesis is that smoking tobacco daily is linked to the elevated risk of individuals to develop psychotic disorders in subjects belonging to case-control and also prospective studies. The second hypothesis is that tobacco smoking is linked to a younger age at the beginning of the psychotic disorder. Lastly, the researchers hypothesized that smoking at a young age is related to the increased risk of psychosis. The researchers also aimed to come up with an estimate prevalence value of smoking in individuals exhibiting their first episode of psychosis.

The researchers from the King's Institute of Psychiatry, Psychology & Neuroscience (IoPPN) collated data from 61 Medline, Embase, PsycINFO and other observational research findings that present the rate of smoking among individuals diagnosed with psychotic illnesses. The researchers were able to collate a total of about 15,000 tobacco smokers and 273,000 non-smokers. They then compared these data to their controls and performed calculated investigations in relation to their hypotheses.

The findings of the study, published in the journal The Lancet Psychiatry, show that 57 percent of the study subjects, who experienced their first psychotic episode, were smokers. The researchers also found that individuals, who had experienced their first episode of psychosis, were three times more likely to be smokers, compared to those in the control groups. Psychotic illnesses also develop in individuals who smoke daily, a year earlier than those who do not smoke.

"Excess dopamine is the best biological explanation we have for psychotic illnesses such as schizophrenia," said Sir Robin Murray, Professor of Psychiatric Research at the IoPPN. "It is possible that nicotine exposure, by increasing the release of dopamine, causes psychosis to develop."

The authors of the study, however, admitted that finding an exact cause of the well-established relationship between smoking and psychosis is difficult. They added that only very few of the meta-analysis they studied included the consumption of other substances such as cannabis, which may also affect the findings.

According to the National Institutes of Health, schizophrenia is a severe, long-term brain disorder characterized by hallucinations, which sometimes trigger the patients to plot harm against self and others. Patients diagnosed with this disabling disorder have a huge tendency of scaring other people, thus withdrawing them from society and developing extreme agitation. Other signs and symptoms of schizophrenia include lack of sense in their words and staying still for hours without talking or moving.

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