long term use can cause a genereal and permanent malaise cause by the synchronization of the alpha brain waves in the frontal lobe of the brain.
Cannabinoidal receptors in the brain and spinal column have been linked to schizophrenia, as these receptors are active in schizophrenics.
All psychedelic drugs have been shown to exacerbate the symptoms and speed the onset of mental illness in individuals who are at risk.
All psychedelic drugs mimic the symptoms of paranoid schizophrenia to some degree, and are usually off by only one or two symptoms.
Acid users can hear a lower range of sounds, cane interperet a lower frequency range of colors, have a higher tlerance for sound volume, have trouble differentiating higher lighte frequency colors, have trouble concentrating on a single idea or task (as shown in the gating exorcize wherein the brain's reaction is measured to two sucesive clicks, normal people had a diminished cerebral response to te second while chrinic acid users showed no difference), and are more passive.
There are psychological risks, even beyond the danger of an ego-shattering bout of paranoia, which is why I can hold an intelligent, two-sided conversation with myself.