WASHINGTON – The Food and Drug Administration warned doctors Thursday about reports of suicidal thinking in some children and adolescents who are taking Strattera, a drug used to treat attention deficit hyperactivity disorder.

Manufacturer Eli Lilly & Co. announced that a black-box warning will be added to the drug’s label in the United States. Such a warning is the most serious that can be added to a medication’s label, and similar warnings will be added to the drug’s labels in other countries. The company said a study showed instances of suicidal thinking were rare.

In a statement, the FDA said it “is advising health care providers and caregivers that children and adolescents being treated with Strattera should be closely monitored for clinical worsening, as well as agitation, irritability, suicidal thinking or behaviors, and unusual changes in behavior, especially during the initial few months of therapy or when the dose is changed.”