Smoking could play a direct role in the development of schizophrenia and needs to be investigated, according to a study published in The Lancet.

The team at King's College London say smokers are more likely to develop the disorder and at a younger age.

Smoking has long been associated with psychosis, but it has often been believed that schizophrenia patients are more likely to smoke because they use cigarettes as a form of self-medication to ease the distress of hearing voices or having hallucinations.

The researchers said nicotine altered levels of the brain chemical dopamine, which has already been implicated in the psychosis.