O'Sullivan was stripped of his Irish Masters title in 1998 after a post-match drug test found evidence of cannabis in his system. He later acknowledged frequent abuse of drugs and alcohol in the early years of his career before he entered rehabilitation in 2000.
"I lost six, seven years to drinking and taking cannabis. Then four years of dealing with stuff away from the table which I didn't deal with very well," O'Sullivan told the BBC on Thursday.
"I wasn't focusing on snooker. But I suppose everyone has those problems, but there's 10 years there where I didn't really do much. I didn't practise much, I didn't have the headspace to win."
O'Sullivan, who won his seventh world title in 2022 but was knocked out in the quarter-finals this year by eventual champion Luca Brecel, said snooker now makes him feel relaxed and calm.
"I always loved my sport and that's what's most important to me. That strips away any temptations of going out," he added.
"I think going to rehab taught me happiness is an inside job, which I truly believe. So since that moment in 2000, I've always believed that."
