It is common for medical therapies to be used off-label in the US. Per the Agency for Healthcare Research and Quality (AHRQ) which is part of the U.S. Department for Health and Human Services, 20% of prescriptions written today are for an off-label use (and some estimates are that off-label prescribing is even more common than that).
https://www.ahrq.gov/patients-consumers/patient-involvement/off-label-drug-usage.html