Heavy cigarette smoking may be a causal factor for schizophrenia development

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cigaretteIt has long been recognized that there is a link between various psychiatric illnesses, especially schizophrenia, and heavy cigarette smoking. However, the reasons why such a link may exist are unclear. This is known as biological plausibility when considering a possible cause-and-effect. One explanation that has been generally accepted (without much in the way of evidence) is that psychotics are attempting to self-medicate distress or are seeking relief from boredom.

A new study published in Lancet Psychiatry found that daily smoking is associated with an increased risk of psychosis and an earlier age at onset of psychotic illness.

The study s authors analyzed 61 previous studies involving almost 15,000 smokers and 273,000 non-smokers. Fifty-seven percent of participants who arrived at mental health services with their first episode were smokers almost three times the percentage of the general population who smoke. The researchers also found that daily smokers developed psychotic illness on average one year earlier than non-smokers.

The authors note that more research is needed to establish a causal link between tobacco use and psychosis. We can t say that we have proof that cigarette smoking causes schizophrenia, said coauthor Sir Robin Murray, professor of psychiatric research at King s College London.

However, coauthor James H MacCabe stated, While it is always hard to determine the direction of causality, our findings indicate that smoking should be taken seriously as a possible risk factor for developing psychosis, and not dismissed simply as a consequence of the illness.

Murray did offer a possible explanation: Dopamine is thought to play a key role in schizophrenia development. Excess dopamine is the best biological explanation we have for psychotic illnesses such as schizophrenia, he said. Murray continues, It is possible that nicotine exposure, by increasing the release of dopamine, causes psychosis to develop.

As a precaution, the authors urge mental health professionals and those working with schizophrenia patients to try to get them to take part in smoking cessation programs.