FDA designations for therapeutics and their impact on drug development and regulatory review outcomes.

New prescription drugs receive approval from the US Food and Drug Administration (FDA) based on tests establishing safety and adequate and well-controlled trials demonstrating "substantial evidence" of efficacy. However, a number of legislative and regulatory initiatives, the most recent being the breakthrough therapy designation created in 2012, give the FDA flexibility to approve drugs on the basis of less rigorous data in situations of greater clinical need. These expedited development and review pathways now contribute to a majority of all new drug approvals and have important benefits in encouraging efficient availability of transformative drugs. They also have a number of risks, including a heightened possibility that the drugs will be discovered to be ineffective or unsafe after widespread use, and confusion by patients and physicians over what it means for a product to be "FDA approved."