The 77-year-old star revealed he and the late Beatles star holed up in a New York City hotel room for a late-night drug binge where they had "mountains of coke coming out of our noses" at 2am.
The "paranoid" pair heard a knock at the door and wondered if it was the police.
However, it was only their pal Andy Warhol, who they refused to allow in because he brought his camera everywhere and they did not want evidence of their drug taking.
Elton John says he took "mountains of cocaine" with John Lennon in a hotel in New York City. (AP PHOTO)
"It took me about five minutes to walk across to the peephole, and I saw it was Andy Warhol," Sir Elton recalls in his new documentary, Elton John: Never Too Late.
"And I went to John, 'Andy', and John went, 'no way'.
"So he kept ringing the bell.
"Like no thanks - that was the fun part of cocaine."
Sir Elton also claimed he was responsible for Lennon reuniting with Yoko Ono after the star's surprise appearance at Sir Elton's Thanksgiving Day 1974 concert at Madison Square Garden.
"If I hadn't told him to do the show, maybe he had never met Yoko again," Sir Elton said.
"Of course, they did get back together and they had Sean (Lennon).
"He became in love again, and so his wildness - he kind of stopped the drugs, stopped the craziness.
"I was happy for him.
"Didn't stop my craziness."
Lennon and Ono first met in London in 1966 and married in Gibraltar in 1969.
They separated for 18 months and reunited in 1974.
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