New York ? 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 finding suggests that about 60 percent of people who have depression can gain 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.