noun
investigational new drug; clinical trial drug
A drug that is being tested in clinical trials and has not yet received marketing approval.
この治験薬はまだ承認されていません。
This investigational drug has not been approved yet.
治験薬の効果を調べるために臨床試験が行われている。
Clinical trials are being conducted to investigate the efficacy of the investigational drug.
新薬 is a new drug that may or may not be in trials; 治験薬 specifically refers to a drug under investigation in a clinical trial.
Compound of 治験 (ちけん, 'clinical trial') and 薬 (やく, 'drug').