Interesting question. The only psychedelic I regularly use is psilocin (mushrooms) so my answers are from a mushroomy perspective, and my knowledge of schizophrenia is purely based on stuff I've read:

Psychedelics do produce symptoms similar to psychosis (i.e hallucinations, delusions, thought disorder). Psychosis is one of the symptoms of schizophrenia, but from what I've read, it seems that psychedelics have more in common with the kind of psychosis that sometimes accompanies the manic episodes of bipolar disorder.

Watch this video from 0:35 to 6:10:

It describes some of these manic psychotic episodes, with symptoms such as:
-oneness, timelessness
-All-knowingness, sacredness
-Delusions / Hallucinations
-Thinking you are dreaming / in a play
-Being tested by God
-You are the Messiah, a prophet, a saint

The experiences described in the video sound very similar to someone who is tripping. They sound very similar to some of the trip reports on the Shroomery.

The biggest similarity between "classic" schizophrenia and psychedelics is probably delusional beliefs. A heavy mushroom trip can give you paranoid delusions, e.g you are on some kind of secret special mission.

However, the hallucinations of schizophrenics seem quite different in character to mushroom-type hallucinations.

Quote:

Chris Frith / Making Up the Mind:
"..there is a very interesting feature of the hallucinations associated with schizophrenia. These experiences are not about the physical world. These people do not just see colors and hear noises. Their hallucinations are about the mental world. They hear voices commenting on their actions, making suggestions and commands."

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Quote:

all those who have had a terrible terrible trip is it anything like this?

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In a word, no. My worst trip felt like I was being lined up for special punishment by God. I have a notebook that describes the experience. The writing tails off about 3 hours into the trip, like those horror/sci-fi movies where people find the video diaries showing the last hours of the doomed videomakers. I remember the phrase "I pray for forgiveness for the ferocity of what I am about to unleash" stuck in my head. There are teethmarks on the notebook, with barely legible writing scrawled across the cover in all directions with GOD I NEED HELP at the centre. The last entries are bizarre and somewhat bleak:

"...more powerful and more violent than anything you have ever seen.."
"...the undigested malice in my steel claws..."
"...my nightmares have gotten out of control..."
"....the fires that are raging in my brain...."
"I can do no more than live with my nightmares and face the consequences."

I was almost literally climbing the walls, I was completely delusional, but apart from the delusional aspect it wasn't an experience that really resembled schizophrenia, at least not how I understand it.

But seeing as I re-dosed with 12g of fresh pans cyans in the middle of an already-difficult trip, it was my own fault it turned into a bit of a nightmare.