"Off-label" use is the use of a pharmaceutical to treat a condition where the FDA has not approved the drug for treatment of that condition, or where the dose or method of administration is not approved.
It is not illegal or even improper for a physician to prescribe a drug for an off-label use, or for a pharmacist to fill such a prescription. It can often be good therapeutic practice to do so. However, in most cases, insurance companies will refuse to reimburse the cost of the drug to the patient. It is illegal for a pharmaceutical company to advertise a drug for an off-label use.It can give rise to legal liability as well if the patient suffers an adverse reaction.
About 20% of prescriptions are off-label, and that figure rises to about 30% in the treatment of psychiatric disorders. However, about three-quarters of off-label use has no scientific support.