Many drugs of abuse and prescribed drugs can cause psychotic symptoms. The associations are also considered in Chapte^...4.,2,3,1l, .ChapieL.4,2,3,.2., Chapter.., 4,2.3.3, Chapje_4,2_._3,4, Chapter.^.^.S.S, Cha£ter_4J2,3,6., CJlaRteí_4,2_._3,Z, Chjper_4_.2,3_.8 and CJhaEter_4,2J3.9. In the context of a differential diagnosis, drugs of abuse—in adolescents and young adults—must be considered. Chronic amphetamine psychosis may be indistinguishable from schizophrenia. The psychosis is florid and may include visual and auditory hallucinations. Phencyclidine (PCP or angel dust) is a drug of abuse in the United States and causes an acute psychosis with prominent affective symptoms as well as perceptual distortions and depersonalization. Other psychotogenic drugs include cocaine, ecstasy, and LSD.
Cannabis is widely used, especially in large metropolitan areas and by certain ethnic groups (e.g. African-Caribbeans); hence an apparent association with schizophrenia may be a chance finding. Cannabis intoxication is more characterized by perceptual distortions and depersonalization than frank psychosis. Clinical experience suggests that cannabis has a propensity to precipitate psychotic relapse in patients with established schizophrenia, although hard data on this issue are lacking.
Delusions and hallucinations may occur rarely during states of alcohol intoxication but are more commonly associated with withdrawal syndromes ( Chapter...4.2,2,3). Alcoholic hallucinosis is a chronic hallucinatory state of uncertain nosological status in which the patient with long-standing alcohol dependence often hears 'voices' which may be derogatory and commenting, in clear consciousness, after a lengthy withdrawal period.
Again the list of agents that can cause psychotic reactions to be distinguished from schizophrenia is very long, and psychotropic drugs are particularly liable to cause psychotic reactions. Two classes of drug deserve mention because of their widespread use and relatively high incidence of major psychiatric adverse effects:
• steroids can cause a wide range of psychiatric disturbances including psychosis
• dopamine agonists used in the treatment of Parkinson's disease and some pituitary adenomas.
Frank psychosis and affective disorders may be seen. In the treatment of neurological diseases, such as Parkinson's disease, and the use of steroids for diseases of the central nervous system, there is often an interaction between the agent and the underlying condition which increases the likelihood of a drug-induced psychosis.
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