Many nursing-home patients who received anti-psychotic drugs between 1976 and 1985 may not have gotten the powerful tranquilizers under current federal guidelines, researchers reported Wednesday.

A study involving almost 9,000 patients at 60 nursing homes in eight Western states found that nearly half of those receiving anti-psychotic drugs lacked diagnosis of a mental illness such as schizophrenia - documentation the federal government began requiring in October.A report on the University of Minnesota researchers' findings appeared Wednesday in the Journal of the American Medical Association.

"It's clearly a widespread practice, but it's not a good one," said Dr. Stephen F. Jencks, a spokesman for the federal Health Care Financing Administration.

A spokeswoman for the nursing-home industry wouldn't discuss the study's specific findings but said nursing homes give anti-psychotic drugs to fewer patients now.

"I think this is a move that began picking up momentum after the federal guidelines came out, but it began before that," said Deborah Cloud, spokeswoman for the Washington-based American Association of Homes for the Aging. "We think that's progress."

Previous studies have indicated anti-psychotic drugs may be widely overprescribed in the nation's nursing homes, a practice some doctors have called a method of chemically restraining patients.

While the drugs counteract some of the symptoms of schizophrenia and other mental illnesses, they also act as heavy tranquilizers.

Excessive use of the drugs could cause side effects including muscular twitches, mental impairment and blood pressure problems, said researchers who conducted the new study.

The study didn't determine whether the drugs were over-prescribed because the new federal guidelines on anti-psychotics weren't in place during the period of the study, said lead author Judith Garrard.

In October, the Health Care Financing Administration began requiring Medicare- and Medicaid-certified nursing homes to document a medical diagnosis of a mental illness before patients begin receiving neuroleptic, or anti-psychotic, drugs.