Smoking may increase your chances of developing schizophrenia or depression, says a study published Nov. 6, 2019, in Psychological Medicine.The team found that people who smoked not only had a higher risk of developing depression and schizophrenia, but that people with either conditions were also more likely to smoke (although the association was not as strong for schizophrenia).Researchers decided to find out using a database containing data from more than 462,000 people, of whom 8% were current smokers and 22% former smokers.It's long been known that people with mental illness are more likely to smoke than those without mental illness.But no one ever looked at what came first -- the smoking or the mental illness.