Tobacco Smoking Raises Schizophrenia Risk, Study Suggests

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British researchers have suggested that smoking tobacco may increase the risk of schizophrenia and other serious mental disorders, based on a new study.

In the study published in the journal Lancet Psychiatry, authors analyzed data from 61 case studies involving tobacco users and non-users, their genetic and environmental factors and their rates of psychosis. The results of the study found that more than half of people who were diagnosed with psychosis were smokers. In addition, smokers were prone to psychosis a year earlier than those who don't smoke.

According to the Guardian, cannabis also causes psychosis and schizophrenia. However, the study authors acknowledged that they can't be sure if the participants in their research are using marijuana. However, James McCabe, co-author of the research, told Reuters that tobacco may be the real culprit and not cannabis since some marijuana smokers combine tobacco to their drug.

"We can't say that we have proof that cigarette smoking causes schizophrenia," psychiatry professor Robin Murray of King's College said in the report. "Indeed it is very difficult to point to any particular factor and say it causes schizophrenia. It is a bit like heart disease—there are a number of risk factors. You inherit some vulnerability and ... are exposed to various things which increase the risk to your life."

Murray added that excess dopamine may be the cause of schizophrenia and other psychotic disorders.

 "It is possible that nicotine exposure, by increasing the release of dopamine, causes psychosis to develop," Murray explained.

Substances that increase dopamine production include nicotine, morphine, cocaine, and amphetamine, according to an article published by the National Institute on Drug Abuse (NIH).

Although the link between psychosis and smoking is unconfirmed, Michael Owen, professor at Cardiff University and director of Institute of Psychological Medicine and Clinical Neurosciences, says that the new study would make "pretty strong case." He added that although the link is hard to prove "without a randomized trial," this could be the start for targeting public health measures to the mentally ill."

With regards to their findings, McCabe reiterated that smoking may be much more than just a bad habit.

"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,"  McCabe said in a report by Daily Mail.