People who smoke may have an increased risk of developing psychosis, a new study has found.

Psychosis refers to a mental state in which a person is detached from reality and experiences a number of abnormal symptoms such as hallucinations, delusions and incoherent thoughts.

It is already widely acknowledged that people with psychosis are more likely to smoke than their peers, but until now it was thought that this was probably due to factors such as stress, boredom, or an attempt to counteract negative symptoms or the side-effects of antipsychotic medication.

Little thought was given to the idea that smoking itself could be increasing the risk of psychosis.

UK researchers carried out a major analysis of 61 studies made up of almost 15,000 smokers and 273,000 non-smokers.

They looked at the rates of smoking among people first presenting with an episode of psychosis and found that 57% were smokers.

The study found that overall, people with a first episode of psychosis were three times more likely to already be a smoker. Furthermore, people who smoked every day and went on to develop a psychotic illness, were found to develop that illness around a year earlier than non-smokers.

According to the researchers, these findings suggest that smoking may have a causal role in psychosis, along with other environmental and genetic factors.

"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," commented Dr James MacCabe of King's College London.

Details of these findings are published in the journal, Lancet Psychiatry.