The strongest warning that the FDA requires is that of the Black Box Warning. This warning is reserved for prescription drugs that pose a significant risk of serious or life-threatening adverse effects, based on medical studies. The Black Box Warning is included in the labeling or medical information of the prescription drug.
Black Box Warnings , powered by Formweb, provides a list of medications with black box warnings, alphabetically and by therapeutic class. This is a proprietary Web site and requires payment of a fee for access.
FDA Drug Safety Web site  allows you to search or browse medications with FDA Safety Alerts; Healthcare Professional, Patient, and Consumer Information Sheets; Medication Guides; and Information Pages.