- The perception of auditory, visual, tactile, or gustatory sensations without an actual stimulus
- Etiology may be from underlying psychiatric disorder or organic cause.
- Bath salts
- Ecstasy (MDMA)
- Lysergic acid diethylamide (LSD)
- Mescaline (peyote)
- N,N-Dimethyltryptamine (DMT)
- Phencyclidine (PCP)
- Psilocybin/Mushroom toxicity
- Chloral hydrate
- Gamma hydroxybutyrate (GHB)
- Toxic alcohols
Other Organic Causes
- Alcohol Withdrawal
- Anticholinergic Toxicity
- Tricyclic (TCA) Toxicity
- Ertapenem Toxicity
Psychiatric Causes 
- Schizophrenia, schizo-affective Disorder
- Parkinson's Disease
- Charles Bonnet Syndrome (in the visually impaired)
- Workup should be targeted toward specific diagnosis. Cranial imaging generally only indicated for focal neurological findings or headache red flags
- In non-auditory hallucinations, assume organic pathology until proven otherwise.
- If concern for suicidal or unknown toxic ingestion:
- Acetaminophen level
- Salicylate level
- Treat the underlying pathology.
- In the case of alcohol withdrawal hallucinosis, no standard therapy has been established, although treatment with neuroleptics (e.g. Haldol) has shown some benefit.  Also continue to treat the alcohol withdrawal.