People with the illness, also called bipolar disorder, swing back and forth between bleak spells of depression and periods of high excitability that may run the gamut from euphoria to rage. From 1.3 percent to 1.5 percent of people in the United States suffer from bipolar disorder, and their risk of committing suicide is estimated to be 10 to 20 times that of the rest of the population.

Perhaps because patients are more likely to seek medical help when they are depressed than when they are manic, the disorder is often misdiagnosed at first as depression alone, but antidepressants are not the correct treatment for bipolar disorder and may in fact make it worse.

The new study, published today in The Journal of the American Medical Association, found that patients taking Depakote were 2.7 times as likely to kill themselves as those taking lithium. Earlier studies by others had also found that lithium could prevent suicide, but today's report is the first to compare suicide and attempted suicide rates in lithium and Depakote users. The study was based on medical records of 20,638 patients aged 14 and older in Washington State and California who were treated from 1994 to 2001.

Solvay Pharmaceuticals, a maker of lithium, paid for the study, but did not influence the findings or the way they were reported, the authors said.

The study included 53 actual suicides and 383 attempted suicides that led to hospitalization. But the researchers, as well as Depakote's manufacturer, cautioned that because this study was based only on patients' records, it was not conclusive.

Precisely how lithium might prevent suicide is not known, although it is believed to help regulate levels of serotonin, a brain chemical that influences mood.

"Lithium is clearly being underutilized," said Dr. Frederick K. Goodwin, the senior author of the study and director of the psychopharmacology research center at George Washington University Medical Center. The drug can save lives, he said, adding, "The real tragedy is that a lot of young psychiatrists have never learned to use lithium."

Lithium, which can smooth out the highs and the lows of bipolar disorder, was first used in the 1950's, and in the 1970's was the first drug to be designated a "mood stabilizer" by the Food and Drug Administration. But the drug has been around for so long that its patent has expired and generic versions exist, meaning that lithium cannot generate substantial earnings for industry, Dr. Goodwin said. Drug companies promote newer, more profitable drugs like Depakote.

Some difficult cases referred to Dr. Goodwin turn out to be people who have never taken lithium because their psychiatrists — often under 40 — never thought of prescribing it. But Dr. Goodwin also emphasized that lithium did not work for everyone and that other drugs were needed..

Dr. John Leonard, a spokesman for Abbott Laboratories, the maker of Depakote, questioned the findings. Dr. Leonard said that studies looking back at patients' records were inherently flawed and not as reliable as studies in which patients were randomly assigned by researchers to take one drug or the other. He said conclusions could not be drawn from the data, and doctors should not base treatment decisions on it.

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