Movies that, so far as I can tell, simulate an Acid Trip.

A Scanner Darkly
This movie was actually made to simulate the experience. The whole thing is rotoscoped, and done on a much grander scale than any other project I can think of. It centers around the near future where a new hallucinogenic drug has swept rampant over the US population. The novel it's based on was written by Philip K. Dick, a cult sci-fi figure who knew firsthand what a trip was like.
As an aside I tried to watch a "documentary" about him today. It was awful, any clever kid with a camera and a computer could have done a better job.
A Scanner Darkly was directed by Richard Linklater, made famous by none other than the quintessential drug movie, Dazed and Confused. This is territory one has to assume he is familiar with.

Fear and Loathing in Las Vegas
Anything Terry Gilliam directs is a little like a drug experience, but this one was also deliberate. Haven't seen it myself, but like A Scanner Darkly, the whole story hinges around drug use. May be the most effective example of "druggies-eye-view".

Spirited Away
I was talking to somebody when I was on my mission, and one of their kids was watching this in the background. I could not focus. Not for anything in the world. It was sooo bizarre, and I've seen more than my fair share of weird movies. I couldn't get over it. How is this conceived of, outside of mind altering chemicals? It probably makes more sense from a Japanese perspective, being familiar with the lore and all. But as an American kid, I pretty readily see drugs.

Chitty Chitty Bang Bang
I know it's a kids movie, but have you watched it since you were a kid? It is very strange. And exceptionally long. Bright colors and nonsense throughout. Did you know it was written by Roald Dahl? Think about James and the Giant Peach for a second. A little boy with a terrible life is offered by a stranger a sack of strange green crystals that will take his worries away? He then sees giant bugs and people in the clouds who paint rainbows? Same kind of thing with Charlie and the Chocolate Factory. A land of candy and fun hidden in the industrial center of the city, managed by a mysterious and eccentric man, whose past we know little about. Not to mention the painted little men. And, if the candy and fun are the euphoria of drugs, the tunnel they float through must be a bad trip.
This is again probably something that has a lot to do with your perspective. But as a twenty first century college kid, again, I see drugs.

Alice in Wonderland
I had a friend freshman year who said that the original Lewis Carrol story was about mathematics and how counterintuitive the world of math could be at times. I'm not much of a mathematician, so I don't really see it. HOWEVER, I can see how the drug culture has latched on to this as one of their own. They wouldn't let us do an "Alice in Wonderland" themed float at my high school due to the potential drug overtones. Alice even ingests some strange stuff in the story, with strange results.
And, of course, I'm looking at this through the lens of a post drug culture kid. Hard not to see it when you're taught from a young age to avoid it.