There are many causes of hallucinations, including: Being drunk or high, or coming down from such drugs as marijuana, LSD, cocaine (including crack), PCP, amphetamines, heroin, ketamine, and alcohol. Delirium or dementia (visual hallucinations are most common). Mental illnesses are among the most common causes of hallucinations. Schizophrenia, dementia, and delirium are a few examples. Substance abuse is another fairly common cause. Some people see or hear things that aren t there after drinking too much alcohol or taking drugs like cocaine or PCP. Drugs like PCP, mescaline, peyote, ecstasy, and even marijuana are considered hallucinogens because they can cause you to hallucinate—you may see things that aren t really there. Two of the most widely used hallucinogens in North America are LSD (“acid”) and Psilocybin (“magic mushrooms” or “shrooms”). Although hallucinations can occur in any sensory form — auditory (sound), visual (sight), tactile (touch), gustatory (taste), and olfactory (smell) — hearing voices that other people do not hear is the most common type of hallucination in schizophrenia.