Background <p>Physician awareness of evidence about off-label uses of prescription drugs can affect prescribing decisions. We tested approaches to disclosing unsupportive data about off-label uses and assessed disclosure impact on perceptions and intentions.</p> Design <p>Primary care providers (PCPs) and oncologists viewed a brief report describing an off-label use of trazodone for insomnia (PCPs) or imiquimod for lentigo maligna (oncologists) and provided their perceptions of its Usefulness and Importance for prescribing decisions, and Intentions to search for additional information about the off-label use. We tested four variations (plus control) of a disclosure about the existence of unsupportive data for the off-label use: complete brief report (specific information about the off-label use), summary plus citation (specific information about the off-label use), citation (general information about the off-label use), and statement that other data may exist (general information about the off-label use).</p> Results <p>Physicians who read any disclosure about the existence of unsupportive data for the off-label use rated the information as more Important for prescribing decisions than those receiving only information about the off-label use (control) (<i>p</i> = 0.01). PCPs reported specific data disclosures were more Useful for prescribing decisions (<i>p</i> &lt; 0.001) than less specific disclosures. Oncologists found all disclosures about unsupportive data Useful but those who read disclosures stating unsupportive data may exist reported greater Intention to search for additional information about the off-label use of the drug (<i>p</i> = 0.03). Frequent off-label prescribing was associated with lower ratings for information Importance for prescribing decisions for both groups (<i>p</i> &lt; 0.05). Prescribing the drug previously was associated with lower ratings of information Importance and Usefulness for prescribing decisions among PCPs (<i>p</i> &lt; 0.001) and greater Intention to search for additional information about the drug (<i>p</i> &lt; 0.001) among oncologists.</p> Conclusions <p>Disclosures about unsupportive data for off-label uses are important and useful for prescribing decisions. Physicians who prescribe drugs for off-label uses more frequently or have prescribed the drug previously may discount the importance of the information. Tailoring the specificity of the disclosure to the needs of the audience may increase its effectiveness.</p>