Why might an approved drug be used for an unapproved use? From the FDA perspective, once the FDA approves a drug, healthcare providers generally may prescribe the drug for an unapproved use when they judge that it is medically appropriate for their patient.
It is estimated that between 40 and 60 percent of all prescriptions written in the United States are for off-label uses. Off-label uses are common, especially for treating cancer, AIDS, pediatric conditions and rare diseases.