Is it permissible to use mushrooms as a psychedelic?
If it’s not, can you tell me why? As it’s not harmful for the body and is even considered a possible treatment for mental health issues (because of the substance psylocybin).

If it is an intoxicant, it is haraam to use. If it just relaxes a person without taking away the ability to make sound decisions it would be okay.

If it is used as a medication it would be okay regardless. However for recreational reasons, it would be haraam if it takes away the intellect.