Effects of substance abuse on hallucination rates and treatment responses in chronic psychiatric patients.

Background: Few data systematically document the effects of illicit drug exposure on psychotic illness. We examined the effect of substance abuse on rates and treatment responses of hallucinations in a chronic psychiatric population.

Method: 113 cooperative patients consecutively admitted to a state psychiatric hospital were administered the Structured Clinical Diagnostic Interview for DSM-III-R, a Hallucination Interview, and an inventory of past and current substances of abuse. Demographic information was obtained on 104 of 108 patients who declined interview. Medication dosage was analyzed for one third of the interviewed sample; hospital records, nursing reports, contacts with relatives, and urine drug screens were used to confirm information from patient interviews. Hallucination rates and response were compared by diagnostic groups (chi-square).

Results: Noninterviewed patients had more frequent hospitalizations, more patients diagnosed with psychosis not otherwise specified or schizoaffective disorder, and fewer females with comorbid substance abuse than the study population. Among interviewed subjects, those with substance abuse and psychiatric illness had first admissions at an earlier age than patients with no substance abuse (p = .005). Schizophrenics experienced higher rates of visual (p = .04) and olfactory (p = .05) hallucinations when using illicit drugs. Substance abuse was associated with decreased treatment responsiveness of auditory (p < .03) and tactile (p < .004) hallucinations in schizophrenic or manic patients. Compared with nonparanoid patients, there was a trend for paranoid schizophrenics with substance abuse to experience more frequent visual (p = .09) and tactile (p = .06) and more refractory auditory (p = .08) hallucinations. No differences in medication dosages were found between patients with treatment-responsive and treatment-refractory hallucinations.

Conclusions: Abused substances may interact selectively with primary psychiatric illness to increase rates and treatment resistance of specific hallucination modalities; etiologies are discussed.