Borg won 66 singles titles, spent 109 weeks as world number one and claimed a record 41 successive wins at Wimbledon.
His retirement at 25 – a time when tennis players are starting to peak – was a shock.
“I had enough. I lost the interest and the motivation,” he said.
“If I knew what was going to happen in the years after, I would continue to play tennis.”
In his autobiography, Heartbeats: A Memoir, co-written with his wife Patricia, the notoriously private Borg speaks about his post-playing career struggles.
“I had no plan. People today, they have guidance. I was lost in the world,” he said.
“There was more drugs, there was pills, alcohol, to escape myself from reality.
“I didn’t have to think about it. Of course it’s not good, it destroys you as a person.”
Borg was taken to hospital after an overdose, external in Milan in 1989 – an incident which made him reassess retirement.
He returned to the tennis tour from 1991 to 1993 but failed to win a single match.
“I was close to dying many times,” Borg added.
“I fixed my life. I’m very happy with myself.”