The 85-year-old comedy legend was "surprisingly ignorant" and was never "interested" in drugs when he was younger, but in 2005, he decided to try the potent hallucinogen - which "can alter a person's perception of reality and vividly distort the senses" - under supervision, and was left in amazement by how "fertile the human mind is".
He told The Times' Weekend magazine: "I just wanted to know what it was all about.
"The man was one of the world experts on it so I felt perfectly safe.
"I got scared for about 10 minutes in the middle, and he and his wife saw me through that.
"But it was extraordinary to realise how fertile the human mind is."
The Fawlty Towers legend has never been much of a drinker either because he wanted to keep a grip on reality.
He said: "I never really wanted to. It wasn't quite losing control … I didn't really want to lose my grasp of reality."
John famously had to pay a £15 million divorce settlement to third wife Alyce Eichelberger in 2008 and the Monty Python star - who was previously married to Connie Booth and Barbara Trentham - now no longer owns any property at all because he transferred ownership of his apartment in Chelsea, London, to his fourth wife, current spouse Jennifer Wade so she could feel "secure".
He said: "The third wife got two properties, one was in London and one was in New York, and we had to sell the other three. I've actually given the flat behind Peter Jones to Jennifer, so I don't have a house, I don't have a car.
"I (did it) to make her feel secure. I think the greatest, saddest thing about our world is how many women feel unsafe … that's not a good society.
"I mean in general, emotionally, they don't feel very secure. And I think if they have a property, they know that I can't kick her out … it's taken anxiety away from her that I think she wasn't totally aware of."
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