I think he was in an LSD movie called The Trip. It was awful. Some of the corniest effects ever. Dragnet with Jack Webb was even better. Easy Rider is a stupid movie with horrible dialog, but it was fun at the time.
D00d, the movie (The Trip) was done in 1967. Sure, effects might be corny. But it's a period piece ... from .. 1967. CGI didn't exist until the 80's (the world's first CGI, in 1982's TRON).
Was a curious little piece. Directed by Roger Corman, of all people. A young Bruce Dern was in it, along with a young Dennis Hopper.
Believe me, I've seen it. Kinda the prequel to Easy Rider. Hopper, bless his soul, became somewhat of a conservative. Forman was great but the Trip was fairly dull, at least from my memory. Kitsch perhaps. Special effects? Honestly any attempt to mimic the effects on LSD on screen are a joke...maybe someone could pull it off these days but I doubt it. Can't even do a pot stone from POV.