You will trip a strange, non-visual, psychedelic trip if you have them and the intoxicants will pass through your body still able to produce the effects.

True.

Supposedly the shamanic method is for the shaman to eat the mushrooms, then the ceremony participants drink the shaman's piss.

I've read that the effects make you feel extremely large, or that the world is shrinking, and that's why it has that effect in Super Mario.