Researchers at King’s College London have published a new study in Lancet Psychiatry which has suggested that smoking cigarettes may increase the risk of psychosis. While previous studies have linked the two together, this study is one of the first of its kind to suggest a cause and effect link.
The research team conducted a meta-analysis of 61 observational studies comprising almost 15,000 tobacco users and 273,000 non users. From these studies, they found that in people presenting with their first episode of psychosis, 57% were smokers.
People with a first episode of psychosis were three times more likely to be smokers than those in control groups. Also, it was found that smokers developed a psychotic illness around a year earlier than non-smokers.
Although this would indicate a causal link between smoking and psychosis, the researchers acknowledge that the exact direction of causality is difficult to determine. In addition, the influence of other potential factors, such as cannabis, were only included in a small number of the meta-studies.
Dr James MacCabe, clinical senior lecturer in psychosis studies, said: “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.”
Professor Sir Robin Murray, Professor of Psychatric Research, commented: “Excess dopamine is the best biological explanation we have for psychotic illnesses such as schizophrenia. It is possible that nicotine exposure, by increasing the release of dopamine, causes psychosis to develop.”
Dr Sameer Jauhar, research fellow, added: “Longer-term studies are required to investigate the relationship between daily smoking, sporadic smoking, nicotine dependence and the development of psychotic disorders.
“In view of the clear benefits of smoking cessation programmes in this population every effort must be made to implement change in smoking habits in this group of patients.”