His psychedelic drug use should be known because much of the art is based on revelations through that:

See this at the page below:

Your father’s work is unquestionably psychedelic; did he take a lot of drugs?
Yes, I suppose he did. He certainly took a lot of acid. He always had mushrooms growing in the house, and stashes of weed in the freezer. But he didn’t have an addictive personality and so it truly was never a problem for him, as it was for many of his contemporaries. He certainly wasn’t high all the time (or at least wasn’t by the time I came along). He would always say “a little bit of everything is good for you, a lot will kill you”.

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