off-label

[awf-ley-buh l, of‐]
adjective Informal.
  1. of, relating to, or denoting a drug prescribed for a particular indication even though the drug has not yet received approval from the Food and Drug Administration for that disease, condition, or symptom.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for off label

off label

adjective, adverb (off-label when prenominal)
  1. (of a prescription drug) relating to use, or being used, in ways for which it has not been approved
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012