Refers to a drug that causes loss of sensation or consciousness, used in medical contexts or for pain relief.
An anesthetic was administered before the surgery.
歯医者で麻酔薬を使ってもらった。
I had the dentist use an anesthetic.
Compound of 麻酔 (masui, 'anesthesia') + 薬 (yaku, 'drug'). The term is a straightforward medical compound.