Finally the largest, most definitive population study of mental illness in this country has demonstrated what many have suspected for years: Many people who drink or who abuse drugs have an underlying mental illness -- and many people suffering from a mental disorder also become alcoholics and drug abusers. Sometimes one leads to another, and sometimes addiction and mental illness seem to stem from a single source.

But the overlap of mental disorders and substance abuse revealed in this study is so striking that the federal government is now moving to redesign the thrust of treatment programs in community mental health centers and substance abuse clinics.

"Unfortunately in this country," said Frederick K. Goodwin, chief of the Alcohol, Drug Abuse and Mental Health Administration (ADAMHA), "the bulk of the mental health treatment system is not sophisticated in the detection or treatment of substance abuse, and the bulk of substance abuse treatment personnel are not tuned in to recognizing mental disorder or treating it."

To Goodwin, the study indicates that it would be "akin to malpractice" for psychiatrists treating mental patients to overlook or ignore a co-existing drug or alcohol problem.

The study also should ring alarm bells for counselors who treat alcoholics and drug addicts. The significant rate of mental disorders among alcoholics and drug abusers may also help explain the high failure rate of treatment programs.

As a result of the study, ADAMHA officials are changing the guidelines for funding treatment and prevention programs. In order for states to get federal funds through the block grant program, mental health and substance abuse projects will "have to include the capacity to diagnose and treat the corresponding conditions," said Goodwin.

Researchers from the National Institute of Mental Health, which is part of ADAMHA, uncovered the extent of the co-existing conditions in their continuing analysis of a special national survey to assess the prevalence of mental problems in the population. Called the Mental Health Epidemiologic Catchment Area survey, the study involves 20,291 people in five cities who were interviewed over a four-year period about their mental health. The new results were reported by Darrel A. Regier, clinical research director of NIMH, and published in the current issue of the Journal of the American Medical Association.

Among the study's most important findings: Half the people with a substance abuse problem also have a diagnosable mental illness. Of those, 26 percent suffer from depression or manic depression, 28 percent have anxiety or panic disorder, 18 percent have a disorder known as "antisocial personality" disorder and 7 percent have schizophrenia. About 37 percent of alcohol abusers have at least one co-existing mental disorder.

Among patients with panic disorder, there is a substance abuse rate of about 36 percent. Among obsessive-compulsives, it's about 33 percent.

People who smoked marijuana were about five times more likely to be schizophrenic, four times more likely to have a depressive or manic-depressive illness and eight times more likely to be classified as having antisocial personality disorder.

In substance abuse treatment centers, the rate of overlapping disorders is higher than in the general population. Roughly 50 to 65 percent of the people in alcohol and drug rehabilitation clinics also have co-existing mental disorders -- probably because in addition to drug or alcohol problems, they have other symptoms that lead them to seek help.

The highest level of co-existing mental and substance abuse problems occurs in prison populations, Regier said. Roughly 90 percent of prisoners with either schizophrenia, depression or manic depression also have a drug or alcohol problem.

Earlier studies have shown that the rate of these mental disorders among prisoners is four times that found in the general population. Indeed, Regier said, according to a recent study, the Los Angeles county jail has more seriously mentally ill people in it than any mental hospital in the country.

The co-existence of mental illness and substance abuse raises special concerns about children and adolescents. An earlier report from the NIMH survey indicated that having a depressive or anxiety disorder in adolescence doubles the likelihood of developing a substance abuse problem later.

Mental health officials believe that a significant number of adolescents with depression or anxiety or both may try to self-medicate with alcohol and drugs instead of seeking treatment for the psychological problem. Going for therapy still carries a stigma, especially for young people, who are particularly sensitive to peer pressure. The tragedy is that anxiety and depression are the most successfully treated of all mental disorders.

Both Regier and Goodwin noted that many people believe that depression is something you should get over yourself.

"People will take pills for a headache, a stomachache, a sleep problem, muscle pain, diarrhea, almost anything you can think about," said Goodwin, "but they're not willing to take a pill for depression. There is much less of a stigma to take a drink."

More than 42 million people -- or one in five Americans over age 18 -- will suffer from a mental problem at some time in their lives. That represents 22.5 percent of the nation's adult population of 186 million. At least one in three Americans with mental disorders -- or approximately 29 percent -- will at some time abuse alcohol or drugs or both.

Twenty-five million Americans -- 13.5 percent of adults -- at some point during their lifetimes will be addicted to alcohol. Among alcoholics, nearly half -- 45 percent -- will have an overlapping mental disorder or be addicted to drugs.

Drug addiction affects 6.1 percent of adults -- 11 million people. More than seven in 10 addicts -- or 72 percent -- will also develop either an addiction to alcohol or a mental disorder or both.

SOURCE: National Institute of Mental Health, Epidemiologic Catchment Area (ECA) Study, 1990