NEW YORK -- The Food and Drug Administration ordered drug makers yesterday to add warnings to antidepressant medications, saying the drugs increase the risk of suicidal thinking or behavior in some young adults.
The drugs' labels, which have included similar warnings for adolescents and children since 2005, will apply to people under 25.
The expanded warnings, which will appear in a black-ruled box displayed prominently on the prescribing information, are the strongest caution that regulators can impose.
The drug agency also recommended that the labels remind doctors to balance this risk against the "clinical need" for treatment and mention that the drugs, which include well-known products such as Paxil and Zoloft, are associated with no increased suicide risk in patients older than 25 and appear to reduce the risk in those older than 64.
About 11 percent of adults younger than 44, or 12 million Americans, received at least one prescription for an antidepressant last year, say estimates by Medco, the largest prescription manager. Census figures suggest that 19- to 24-year-olds could make up about a fourth of that group.
Dr. Thomas Laughren, director of the division of psychiatry products in the drug agency, said yesterday that the new labels were meant to balance the value of the drugs against the risk in young adults, "which is quite small. But it's real and should be paid attention to."
It is unusual for warning labels to mention benefits such as the lower risk of suicide in older adults, but the mixed message reflects the yearslong debate over the risks and benefits of antidepressants, specialists said. It also reflects concerns that the debate, and the headlines it has generated, have scared consumers and doctors away from medications that could help, the specialists said.
In 2004, when the agency began publicly debating suicide risks for minors taking antidepressants, children's-prescription rates tapered off. In that year, the suicide rate among adolescents rose significantly for the first time in more than 10 years, and some specialists say the trends are linked.
The labeling changes follow the recommendations of an advisory panel of outside specialists, including psychiatrists and consumer representatives, that met in December. That panel heard scientists, as well as dozens of other people who told of loved ones who had committed suicide after having been prescribed antidepressants.
The drug agency reached its conclusions after analyzing 295 antidepressant studies, including 77,000 adults from college students to retirees. The analysis found no increased risk of completed suicides in patients taking the medications.
But 21 suicide attempts were reported among the 3,810 19- to 24-year-olds taking the drugs, working out to a 0.55 percent risk, twice the risk in adults of the same age who took placebo pills, the analysis found.
By age 25, the risk was not significantly different, the agency said. The agency said it did not know why the risk would drop suddenly after age 25. But neuroscientists say there is some evidence that brain development continues into the early 20s.
"The peak rate for suicidal behavior is between 16 and 25, and it's possible that because of the magnitude of the behavior they're picking it up" in the analysis, said Dr. David Brent, a professor of psychiatry at University of Pittsburgh Medical Center.
For all its careful language, the label change may stir more passion in a debate that has become one of the most bitter in modern medicine, some specialists said.
Dr. David Healy, a psychiatrist at the University of Cardiff in Wales who was among the first to raise questions about the drugs' suicide risk, said that the new warnings were overdue and that the risk was not likely to disappear suddenly at age 25.
"It has been dismaying to see the delay in formally recognizing this risk, whose recognition can only make the use of these drugs safer for those who really need them," Healy said in an e-mail message. "The clinical trial data pointing to a risk was compelling 17 years ago."
Healy has been a paid consultant to plaintiffs' lawyers in lawsuits against drug makers.
Dr. Kelly Posner, an assistant professor of child psychiatry at Columbia University who helps the drug agency analyze suicidal behaviors, said the studies were not structured to assess suicide risk and could not determine the cause of the behavior.