Painkiller, Pain Reliever, Sedative, Tranquilizer, Tranquiliser
noun
Tranquilize your pain with a strong dose of painkillers! Yum yum. Don't take too many though!
ちんつうざい
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
医者に鎮痛剤を注射してもらいました。
I received a shot of the painkiller from the doctor.