[Addiction and schizophrenia. Nosological, clinical and therapeutic questions. 2. Substance dependence and schizophrenia].

While schizophrenia-like psychosis is known to occur with chronic alcoholism the nosological differentiation of schizophrenia-like psychosis in patients with drug abuse remains difficult. An increased risk for the development of such psychoses has been discussed for various substances, e.g. cannabis. On the one hand this is supported by clinical and epidemiological studies but a final agreement has not been reached. On the other hand high prevalence estimates for substance abuse in schizophrenics have been reported in the angloamerican literature. Prevalence estimates for drug abuse and dependence range between 7-65% and a comparatively distinct abuse pattern in schizophrenics has been discerned: Apart from alcohol schizophrenics tend to abuse cannabis and psychostimulants including cocaine and hallucinogenes, whereas narcotics are abused only infrequently. Whether these recent figures for substance abuse and dependence are due to a real increase (32) or to improved diagnostic instruments and differences in the classification of psychiatric disorders or to selected samples (3, 122) is still a matter of controversy. In comparison with other schizophrenics dual diagnosis schizophrenics show more positive (psychotic) and less negative symptoms. In this review some clinical and neuro-biological problems concerning the concept of drug-induced psychosis and basic principles of pharmacotherapy and psychotherapy in schizophrenic patients with substance abuse are discussed.