Experts at King's College London say that although links have been noted before between tobacco use and psychosis, there's been little research into the possibility that smoking can cause schizophrenia.
Past studies have looked at why people with psychotic conditions smoke. Explanations have included relief from boredom or distress and a desire to self-medicate.
Reviewing the Evidence
To explore the subject further, 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.
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.
"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,” says Michael Bloomfield, MD, clinical lecturer in psychiatry at University College London. "Anyone who needs help in stopping smoking should speak with their doctor."