Once medical drugs and devices are approved for marketing by the FDA they can legally be used for purposes and in ways other than the ones for which they have been tested and approved. However, it is illegal for manufacturers to advertise or promote such unapproved uses of the drugs and devices. Part 1 of this review focuses on off-label use of FDA-approved therapies. Part 2 addresses illegal off-label marketing of drugs and devices. While off-label use can be beneficial to patients, unless carefully undertaken off label use may undermine the important safety mission of the FDA, can expose patients to elevated risks without proven benefits (or possibly no benefit), and can reduce motivation of companies to study the safety and risks of off-label use of therapies. These problems are further amplified when off-label use occurs among very vulnerable patient populations such as the elderly, patients with mental health disorders, pregnant women and pediatric patients. This review considers ethical issues in off-label use, as well as important steps for physicians considering an off-label prescription of a drug or device.