Does smoking increase the risk of developing psychosis?

By Kate Bass, B.Sc.Jul 10 2015

Research conducted at King’s College London and reported in The Lancet Psychiatry today indicates that smoking is associated with an increased risk of developing psychosis; a mental health disorder that disrupts normal processing by the brain causing delusion and hallucination.

Smoking tobacco has long been associated with psychosis, and particularly schizophrenia, but today the nature of that association has changed. It was thought that smoking was common among patients with psychotic illness because they were using cigarettes to help ease the pain of distressing beliefs and the frustration or anxiety stemming from persistent hallucinations. However, the latest research indicates that smoking cigarettes may actually increase the risk of developing psychosis in the first place.

Researchers analysed data from 61 observational studies of almost 15,000 tobacco users and 273,000 non-smokers. They found that more than half (57%) of patients presenting with a first episode of psychosis were cigarette smokers. Furthermore, people with a first episode of psychosis were three times more likely to be smokers than those who did not develop psychotic illness. It was also apparent that among those who had psychosis, the illness developed around a year earlier in people who smoked daily compared with non-smokers.

Dr James MacCabe, Clinical Senior Lecturer in Psychosis Studies at King’s College London, commented:

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".

Having identified this association between smoking and the development of psychosis, further research is needed to understand the basis of this association and to confirm its validity. It is not known whether many of the patients included in the analysis were using other substances in addition to tobacco, such as cannabis. However, the association with tobacco is plausible and justifies further investigation since psychotic illnesses are characterised by high levels of the neurotransmitter dopamine, and nicotine exposure increases the release of dopamine.

Dr Sameer Jauhar, Research Fellow at King’s College London explained:

Longer-term studies are required to investigate the relationship between daily smoking, sporadic smoking, nicotine dependence and the development of psychotic disorders".

Since there are already clear benefits of smoking cessation programmes, particular effort should be made to encourage a change in smoking habits in patients at risk of developing or suffering from psychosis.