Eminem's handlers were concerned his drug addiction hell had caused the star lasting "brain damage" because he almost forgot how to rap as he recorded his 2009 album Relapse.

The Lose Yourself hitmaker forced himself to kick his longtime substance abuse habit after suffering a near-fatal drug overdose in 2007, and got back into the studio to work on songs for the follow-up to 2004's Encore.

However, Eminem was still trying to adjust to life without the use of prescription drugs and as such, he isn't proud of any of the music he put out on Relapse.

"I certainly have not had a perfect career. I've put out bad albums," he told Vulture. "Encore was mediocre, and with Relapse - it was the best I could do at that point in time. (Relapse) was a funny album for me because I was just starting back rapping after coming out of addiction.

"I was so scatterbrained that the people around me thought that I might have given myself brain damage. I was in this weird fog for months. Like, literally I wasn't making sense; it had been so long since I'd done vocals without a ton of Valium (anxiety medication) and Vicodin (painkiller). I almost had to relearn how to rap."

To mask his struggles, Eminem put on a string of odd accents for tunes on Relapse, and at first, his manager Paul Rosenberg was unaware of how strange it all sounded.

"I recorded at least 50 to 60 songs for that album and on each one I would get a little more drastic with the accents, trying to bend the words and make them rhyme in ways they wouldn't if you just said them regular (sic)," the 45-year-old said. "It was this gradual thing and I didn't even realise how accent-heavy the album got. Paul didn't realise it either until he went and played the music for somebody at (his record label) Interscope and they were like, 'Why is he doing all those accents?' So yeah, I don't know how much replay value that album has."

Eminem was able to redeem himself with 2010's Recovery, which won the Best Rap Album Grammy Award in 2011.

His eighth studio album, Revival, hit retailers on Friday (15Dec17).