Off-label prescribing refers to the use of an FDA-approved medication for an indication, population, dosage, route of administration, or duration that is not included in the drug's approved labeling. The FDA approval process evaluates drugs for specific indications through a phased clinical trial system: Phase I (safety and pharmacokinetics in healthy volunteers), Phase II (efficacy and dosing in small patient groups), and Phase III (large randomized controlled trials confirming efficacy and monitoring adverse effects). FDA approval represents the minimum evidence threshold for marketing a drug for a specific indication, but it does not restrict licensed prescribers from using the drug for other evidence-supported purposes. Approximately 20% of all prescriptions in the United States are written for off-label indications, and in certain populations — particularly pediatrics, oncology, and psychiatry — the rate exceeds 50-80% because manufacturers often lack financial incentive to pursue additional FDA indications through costly clinical trials. The pharmacological rationale for off-label prescribing rests on understanding that a drug's mechanism of action often has therapeutic implications beyond the initially studied indication: gabapentin's calcium channel modulation (approved for seizures) provides...