Rates of smoking, drinking and substance use are higher in patients suffering from mental illness when compared with general population, a new study has found.

The study was conducted by researchers at the Washington University School of Medicine in St. Louis along with their colleagues at the University of Southern California.

The team looked at the data from 20,000 people, including 9,142 psychiatric patients who were diagnosed with schizophrenia, bipolar disorder or schizoaffective disorder.

People suffering from schizoaffective disorder have psychotic symptoms such as hallucinations and delusions along with mood swings, according to a press release.

The team also looked at smoking, drinking habits of 10,000 people who weren't diagnosed with any mental condition.

Results of the study are as follows:

  • 30 percent of people with severe psychiatric illness regularly binged on alcohol when compared with 8 percent of people with no history of mental illness. Binge drinking is when a person drinks four servings of alcohol in a single session.
  • 75 percent of the mentally ill were regular smokers when compared with 33 percent of the general population.
  • 50 percent of the mentally ill people used marijuana versus 18 percent of the general population.
  • 50 percent of the psychotic patients also used illicit drugs when compared with 12 percent of non-psychotic population.

"These patients tend to pass away much younger, with estimates ranging from 12 to 25 years earlier than individuals in the general population," said first author Sarah M. Hartz, MD, assistant professor of psychiatry at Washington University.

"They don't die from drug overdoses or commit suicide - the kinds of things you might suspect in severe psychiatric illness. They die from heart disease and cancer, problems caused by chronic alcohol and tobacco use," Hartz said in a news release.

The study was published in the journal JAMA Psychiatry.                                                          

Previously, it was assumed that people with mental disorders use tobacco and other substance to self-medicate themselves. However, last year a study found that brains of these people are more vulnerable to addiction than the brains of other people.