The use of a drug to treat a condition for which it has not been approved by the U.S. Food and Drug Administration (FDA), especially when such use may relieve unpleasant symptoms, or prove compassionate. During the drug approval process in the U.S., drug manufacturers present carefully accumulated data to the FDA about the safety and effectiveness of their products. Drugs are labeled for specific uses when manufacturers make an application to the FDA with data that describe their drug’s performance during clinical trials. If the data withstand rigorous scrutiny the drug is labeled for a specific use. Drug effects that have been observed but not specifically proven (and for which no application has been made) may be exploited for unproven or “off label” uses by licensed medical practitioners.