Justin Bieber has quit taking stimulant Adderall to ease his concentration struggles, amid fears it was fuelling his anxiety issues.

The Baby star reveals he had been taking the prescription drug, typically used to treat attention deficit hyperactivity disorder (ADHD), for "about a year", but he recently ditched the medication because his doctors worried he was becoming too reliant on the substance.

"I've been getting a lot of anxiety, and they think it's stemming from the Adderall," he told GQ magazine. "That's why I've stopped taking it. Or else I wouldn't stop, because I really enjoy it."

During the candid cover interview, Justin also discussed his renewed relationship with God, insisting he wouldn't have been able to put his past bad behaviour behind him if it wasn't for his Christian faith.

"I feel like that's why I have a relationship with Him, because I need it," he explained. "I suck by myself. Like, when I'm by myself and I feel like I have nothing to lean on? Terrible. Terrible person.

"If I was doing this on my own, I would constantly be doing things that are, I mean, I still am doing things that are stupid, but... it just gives me some sort of hope and something to grasp onto, and a feeling of security, and a feeling of being wanted, and a feeling of being desired, and I feel like we can only get so much of that from a human."

The singer is currently enjoying a career comeback after taking a hiatus during his late teens, during which he developed a reputation as a bad boy following a number of legal issues and run-ins with police.

Among his many headline-grabbing incidents, he was arrested for driving under the influence in Florida in January, 2014 - the same month he was accused of vandalising his former neighbour's Calabasas, California home.