A study suggests that chemicals in tobacco may help trigger serious mental illnesses such as schizophrenia.
New research shows that smoking can triple the chances of developing psychosis.
Scientists believe something in tobacco might actually be responsible, alongside genetic and environmental influences.
The researchers analysed data from 61 observational studies involving almost 15,000 tobacco users and 273,000 non-users.
They found that 57 per cent of people treated for a first episode of psychosis were smokers. Psychotic patients were three times more likely to consume tobacco than individuals without severe mental illness.
The study also showed that daily smokers became psychotic around a year earlier than non-smokers.
Dr James MacCabe, a member of the team from King’s College London, 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.”
The scientists, whose findings are reported in The Lancet Psychiatry medical journal, acknowledge that causality is difficult to prove.
One theory is a possible link between smoking and excess dopamine, a brain chemical that plays a role in transmitting nerve signals.
Professor Sir Robin Murray, from the Institute of Psychiatry, Psychology and Neuroscience at King’s College, said: “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.”
A proven link has already been found between cannabis use and psychosis in genetically vulnerable people.
“However, much more research is needed before scientists can say for certain that smoking definitely increases the risk of schizophrenia since it remains possible that people who would go on to develop schizophrenia are more likely to start smoking.
“Regardless of these findings, there is overwhelming evidence that nicotine use through tobacco smoking is one of the most dangerous drug problems in the world. Anyone who needs help in stopping smoking should speak with their doctor.”