The song was released on 1 May 2019 as the lead single from his second extended play, Free Time.

[1] The song sees Ruel reunite with producer M-Phazes and Sarah Aarons (whom he had both collaborated with on his 2017 EP Ready), and collaborate with songwriter Hiren Mor for the first time.

[5] Sose Fuamoli from Triple J said the song is "marked by bold bass and melodic work", saying "'Painkiller' is a track that sees Ruel step into a more mature songwriting space, leaning more into rich R&B notes and letting his natural cadence and rhythmic notes flourish.

His soul and jazz influences bleed through on this single too, finding and connecting with that bass groove with ease.

"[6] Alissa Arunarsirakul from Ones to Watch said "'Painkiller' is drenched with warm violins, groovy bass lines, and luscious vocals".