Smoking linked to psychosis

Jul 10, 2015, 5:04 PM EDT
Close up of womans face obscured by cigarette smoke
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A study published in Lancet Psychiatry found that people with schizophrenia are three times more likely to smoke than those who don't have the condition. Researchers reviewed 61 studies that included nearly 15,000 tobacco users and 273,000 non-users. They found that 57% of people diagnosed with schizophrenia for the first time were smokers. WebMD reports:

Also, people who were diagnosed for the first time were three times more likely to smoke than those who hadn't had schizophrenia.
A possible explanation is that heavy cigarette smoking increases the ability to make the chemical dopamine in part of the brain. Dopamine is thought to play an important role in the development of schizophrenia.
The Role of Dopamine
"Excess dopamine is the best biological explanation we have for psychotic illnesses such as schizophrenia,” says Robin Murray, professor of psychiatric research at King’s College London, in a statement. “It is possible that nicotine exposure, by increasing the release of dopamine, causes psychosis to develop."
The authors say it's hard to prove from available research that smoking tobacco actually causes schizophrenia. For instance, they were unable to filter out the effects of other substances, such as marijuana.
Still, as a precaution, co-author Sameer Jauhar urges people working with schizophrenia patients to try to get them to take part in smoking cessation programs.
Dr James MacCabe, from the Institute of Psychiatry, Psychology and Neuroscience at King's, said: "It's very difficult to establish causation [with this style of study], what we're hoping that this does is really open our eyes to the possibility that tobacco could be a causative agent in psychosis, and we hope this will then lead to other research and clinical trials that would help to provide firmer evidence."
Clearly most smokers do not develop schizophrenia, but the researchers believe it is increasing the risk.
The overall incidence of the condition is one in every 100 people normally, which may be increased to two per 100 by smoking.
The researchers said nicotine altered levels of the brain chemical dopamine, which has already been implicated in the psychosis.
Prof Michael Owen, the director of the Institute of Psychological Medicine at Cardiff University, said the researchers had made a "pretty strong case" that smoking may increase the risk of schizophrenia.
"The fact is that it is very hard to prove causation without a randomised trial, but there are plenty of good reasons already for targeting public health measures very energetically at the mentally ill."