The study by researchers at Washington University School of Medicine in St Louis and the University of Southern California is the largest ever assessment of substance use among people with severe psychiatric illness. (Agencies)
The finding is of particular concern because individuals with severe mental illness are more likely to die younger than people without severe psychiatric disorders, researchers said.
"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, 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.
The study analysed smoking, drinking and drug use in nearly 20,000 people.
That included 9,142 psychiatric patients diagnosed with schizophrenia, bipolar disorder or schizoaffective disorder- an illness characterised by psychotic symptoms such as hallucinations and delusions, and mood disorders such as depression.
The investigators also assessed nicotine use, heavy drinking, heavy marijuana use and recreational drug use in more than 10,000 healthy people without mental illness.
The researchers found that 30 percent of those with severe psychiatric illness engaged in binge drinking defined as drinking four servings of alcohol at one time. In comparison, the rate of binge drinking in the general population is 8 percent.
Among those with mental illness, more than 75 percent were regular smokers. This compares with 33 per cent of those in the control group who smoked regularly.
There were similar findings with heavy marijuana use: 50 per cent of people with psychotic disorders used marijuana regularly, versus 18 per cent in the general population.
Half of those with mental illness also used other illicit drugs, while the rate of recreational drug use in the general population is 12 per cent, researchers said.
The study is published in the journal JAMA Psychiatry.
The study by researchers at Washington University School of Medicine in St Louis and the University of Southern California is the largest ever assessment of substance use among people with severe psychiatric illness.