The FDA said children taking Strattera should be closely monitored for worsening symptoms, agitation, irritability, suicidal thinking or behaviors and behavior changes.

Lilly will add the warning to label worldwide for Strattera, for which the US Food and Drug Administration issued a health advisory Thursday after reviewing clinical trial data submitted by the company.

Lilly said that reports of suicidal thoughts by children and adolescents taking the drug were rare. Details on the labeling are being worked out with the FDA, along with regulators in Europe and Australia.

FDA officials said in addition to the black-box warning -- the most prominent of medication warnings -- the Indianapolis-based company will also have to develop a medication guide for patients and health care providers.

Increased Suicidal Thoughts

Dr. Thomas Laughren, director of the FDA's division of psychiatry products, said in December the federal government asked Lilly to review 13 clinical trials conducted on children to assess a suicide risk.

"The risk for any individual patient taking this drug is quite low, but from a public health standpoint, four (case) per thousand is a fairly big signal, given there are tens of thousands of patients taking this drug," Laughren said. "We do think that prescribers and patients need to be aware of this risk that we've just discovered."

About 2 million patients -- adults and children -- have been prescribed Strattera since it became available.

The FDA said Lilly submitted results from a Strattera clinical trial of 1,357 youths taking the medication that found five of them had increased suicidal thoughts, while none of 851 youths taking a placebo showed such changes. Lilly said one youth attempted suicide during its Strattera trials, but that researchers saw no signs of increased suicidal thoughts among adults.

Strattera won praise from some doctors and parents when it became available in 2003 as an attention deficit disorder (ADD) and attention deficit hyperactivity disorder (ADHD) treatment because, unlike Ritalin, it is not a stimulant, a class of drug that can be addictive.

But its chemical makeup is similar to certain antidepressants, which last year were found to have a connection to an increased risk of suicide.

Sales Have Dropped

ADHD affects as many as 7 percent of school-aged children and 4 percent of adults in the US.

The FDA said children taking Strattera should be closely monitored for worsening symptoms, agitation, irritability, suicidal thinking or behaviors and behavior changes.

Strattera's worldwide sales have dropped lately, falling 31 percent to $123.5 million during this year's second quarter from a year earlier.

"Lilly continues to view Strattera as a safe and effective treatment option," Alan Breier, the company's vice president and chief medical officer said. "Those doing well on the medication should be able to continue their treatment with confidence."

Lilly warned doctors in December to stop using Strattera in patients with jaundice or who show signs of liver problems, and it placed a boldface warning on the label and in prescribing information after at least two patients on the medication developed liver problems.

Lilly shares rose 4 cents to $53.51 in late morning trading on the New York Stock Exchange.