The next time your doctor writes you a prescription, consider this: The medication may not be approved for your specific condition or age group.

But you probably shouldn't call the medical board. The practice, called "off-label" prescribing, is entirely legal and very common. More than one in five outpatient prescriptions written in the U.S. are for off-label therapies.

"Off-label" means the medication is being used in a manner not specified in the FDA's approved packaging label, or insert. Every prescription drug marketed in the U.S. carries an individual, FDA-approved label. This label is a written report that provides detailed instructions regarding the approved uses and doses, which are based on the results of clinical studies that the drug maker submitted to the FDA.

“Many people may be surprised to know that the FDA regulates drug approval, not drug prescribing, and ... doctors are free to prescribe a drug for any [reason they think is medically appropriate],” says G. Caleb Alexander, MD, MS, a medical ethics advocate and assistant professor of medicine at the University of Chicago Medical Center. "Off-label use is so common, that virtually every drug is used off-label in some circumstances."