Clinical and regulatory features of drugs not initially approved by the FDA.

US Food and Drug Administration (FDA) denials of New Drug Applications (NDAs) are often controversial, yet little is known about the basis and characteristics of these decisions. We reviewed new drugs and biologics evaluated by FDA advisory committees between 2007 and 2009 and found that half (27/52, 52%) were unapproved in the first cycle. By 2013, 63% had been approved. Products with initial safety concerns (62%) were much more likely to be approved eventually than drugs with efficacy concerns (8%).