Simple Creatures is a collaboration between the members of two pop-punk bands, blink-182's Mark Hoppus and All Time Low's Alex Gaskarth. This was the first song they wrote together. It was released as their debut single after it got the thumbs up from close friends.

"In the studio it felt immediately like it was the song that best defined Simple Creatures," Gaskarth told Kerrang. "It's gritty, grimy, rooted in the musicality we both came up on, but with a twist that takes it away from anything we've worked on before."

The track is about being destroyed by the things you love. Gaskarth explained: "'Drug' is a song about someone or something you want the most, being terrible for you… Feels great until it doesn't, but then you can't stop."