Pop star Justin Bieber, who battled substance abuse as a teenager, says he used to take drugs to ease the pain because he was not satisfied with what he had achieved.

"There was a sense of still yearning for more. It was like I had all this success and it was still like: `I`m still sad, and I`m still in pain. And I still have these unresolved issues.` And I thought all the success was going to make everything good. And so for me, the drugs were a numbing agent to just continue to get through," Bieber said in an interview with GQ Magazine, reports femalefirst.co.uk.