investigational new drug

noun

in·​ves·​ti·​ga·​tion·​al new drug in-ˌves-ti-ˈgā-shə-nəl- 

: a drug that has not been approved for general use by the Food and Drug Administration but is under investigation in clinical trials regarding its safety and effectiveness first by clinical investigators and then by practicing physicians using patients who have given informed consent to participate

—abbreviation IND

called also investigational drug