NEW YORK (AP) – The large group of depression sufferers who haven’t recovered with two common medications stand little chance of success from a third drug, says the latest report from the nation’s most ambitious study of depression treatment.

Only about 16 percent of those in the study became free of symptoms after switching to a third drug, researchers said.

Combined with previous reports from the project, the new finding suggests that about 60 percent of people who have depression can gain complete remission by the time they’ve tried three drugs. Each year, about 14.8 million American adults struggle with depressive illness.

The six-year, $35 million treatment project has yet to publish its findings from further treatment attempts, including trying a fourth drug.

The 16 percent success figure for trying a third drug is quite modest, but “you still have a chance,” said Dr. Maurizio Fava of Massachusetts General Hospital, lead author of the new report in the July issue of the American Journal of Psychiatry.

The finding also suggests that patients should talk to their doctors about other strategies, like taking a combination of antidepressants or boosting the effect of an antidepressant by also taking a different kind of drug, he said.

Fava said that maybe 30 percent to 50 percent of depression patients treated with antidepressants will need to try a third drug.

The 16 percent success rate is “pretty consistent with what we’ve believed before,” said Dr. Matthew Menza of the Robert Wood Johnson Medical School in New Jersey, who was not involved in the research.

The study followed 235 people who hadn’t gained complete relief from the project’s first two attempts to treat them, or who couldn’t tolerate the treatment.

All had started out with Celexa, made by Forest Laboratories and one of a widely used class of drugs called SSRIs. If that didn’t work, they either switched to another antidepressant or continued with Celexa and added a second drug.

For the third attempt, they were randomly assigned to take either mirtazapine or nortriptyline, which are sold in generic form by several companies.

After 14 weeks of treatment, symptoms had disappeared in 12 percent of the mirtazapine users and 20 percent of nortriptyline users. The difference in rates was not statistically significant, but Menza called it a “tantalizing” hint that perhaps older drugs like nortriptyline might be worth a renewed look by doctors.

Menza noted that the overall project did not test some drugs that have emerged as possibilities since the research was begun. “We have a lot of interesting new treatments now,” he said. “We’re left today with the impression these things are probably useful, but we’re sometimes wrong.”

Dr. Thomas Insel, director of the National Institute of Mental Health, said the overall project shows that “we need new and more effective antidepressants.”

It also shows that scientists must find ways to predict which patients will respond to particular drugs, and researchers have begun to find clues by studying the DNA of study participants, he said.

“That kind of information will really be very important to us as we got forward and try to make sense of how do we personalize care for depression,” he said. “That’s the future here.”

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Study information: http://www.star-d.org