This AHRQ-funded study discovered that 40% of patients received a medication that carried a potential for serious harm, classified by an FDA black box warning (BBW). Using a retrospective method to analyze nearly 1 million automated claims data, investigators determined the above prescribing rate for 216 specific BBW drugs in diverse ambulatory settings. While the authors acknowledge significant variability in compliance with BBW medications, the warnings themselves failed to prevent their use in many circumstances. Additional systems need to complement the BBW labeling practice, as certain clinical situations may lead to a lack of compliance with such guidelines. Improved information about risk, determination of risk, and methods to modify prescribing behavior will move clinicians closer to desired goals of medication safety.