"Oxytocin" is a song by American singer-songwriter Billie Eilish, the fifth track on her second studio album Happier Than Ever (2021). Eilish wrote the song with its producer―her brother Finneas O'Connell, who provides backing vocals. A dance, EDM, electronica, electropop, industrial pop and techno song, "Oxytocin" was the last track created for the album. While composing it, Eilish aimed to make it sound "insane" when performed live, envisioning sex imagery for the lyrics.