"I've been helping Eminem over the last 18 months and he's doing brilliantly," John says, reports the British Press Association.
In May, Eminem admitted he'd suffered from a devastating drug addiction that led to him downing as many as 20 Vicodin, Ambien and Valium in a day.
"The numbers got so high," he told Vibe magazine, "I don't even know what I was taking.
Following his first stint in rehab in 2005, the rapper, 37, said he nearly overdosed after an acquaintance gave him unidentified blue pills, which a doctor later told him were actually methadone.
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