The English rock great, who brought his touring career to an end last year and has been sober for 34 years, has helped fellow celebrities including Eminem and Robbie Williams to recover from addiction.
Elton told Time magazine that it is "tough to hear" how bad your behaviour has become, and said admitting this helped him get clean.
He added that marijuana is "addictive", and said: "It leads to other drugs. And when you're stoned - and I've been stoned - you don't think normally.
"Legalising marijuana in America and Canada is one of the greatest mistakes of all time."
In a 1999 interview with David Frost, Elton disclosed that his throat problems midway through an Australian tour in the mid-1980s were caused by marijuana, and said he had given up using the drug after advice from doctors.
In Canada, cannabis is legal from the age of 18, with certain restrictions including the amount people can possess and distribute.
Certain US states including California have restrictions on running a cannabis business, and it has been legal for recreational use for people aged 21 and over since 2018.
Elton also discussed his "short fuse", saying he can snap "if I'm tired, if I'm exhausted, if I'm overwhelmed", which was explored in a 1990s documentary titled Tantrums And Tiaras.
Shot over a year by his husband David Furnish, it showed how Elton often became frustrated, and nearly pulled out of a video shoot because his clothes were late.
"I don't like having that temperament, but it's all usually done and dusted within five or 10 minutes," he said.
Elton credits the short fuse for him creating songs quickly, saying: "But it's really effortless. If I get a lyric and I look at it, the song comes straight out."
Directors Furnish and RJ Cutler are putting out a new documentary, Elton John: Never Too Late, which captures the veteran singer preparing for his final concert in North America at Dodger Stadium in Los Angeles.
Elton disclosed in September that his vision had been affected in his right eye after he contracted an infection.
Lifeline 13 11 14
Butterfly Foundation 1800 334 673
