Justin Bieber has written an emotional essay about how he became "the most hated person in the world" thanks to a string of "bad decisions" in his 20s.

The star, who was discovered by music manager Scooter Braun when he was 13, admitted to heavy drug use and abusing his relationships.

"I became resentful, disrespectful to women and angry," he wrote.

"I became distant to everyone who loved me... I felt like I could never turn it around."

The Canadian star, who has been candid about his mental health struggles, explained how the constant praise he received in his teens had distorted his perspective on life.

"I went from a 13-year-old boy from a small town to being praised left and right by the world, with millions saying how much they loved me and how great I was," he said.

"You hear these things enough as a young boy and you actually start believing it."

"Everyone did everything for me, so I never even learned the fundamentals of responsibility," he explained on Instagram.