The relationship between drug abuse and vulnerability for psychosis still remains insufficiently understood. A proportion of the schizophrenia syndrome could be due to drug abuse in the absence of genetic vulnerability. The objective is to test the association between drug abuse and attention endophenotype in schizophrenia.

One cross-sectional study was carried out in a sample of 70 schizophrenia in-patients in acute state. It was defined two groups of schizophrenia patients: with (n=25) and without (n=45) drug abuse. The attention endophenotype was measured using CPT (X version, d prime parameter). It was controlled for: general neuropsychological performance (Trail Making Test A and B, Stroop Test), symptoms (PANSS, SANS, SAPS), basic symptoms (FCQ-III), clinical global impression, functioning (GAF), treatment, extrapyramidal side effects and akathisia. After Z-score transformation, performance in CPT was compared between the two groups using the student's t test. When necessary we used regression models for the adjustment of control variables.

Schizophrenia patients with drug abuse had a better performance in CPT (effect size: 0.71; p=0.004). Both groups were comparable in terms of the control variables except for Trail Making A, but when controlling for this variable the difference remains significant. Nevertheless, Trail Making Test is linked to attention process, so the differences can be explained by the different performance in both groups.

Schizophrenia patients with drug abuse had less genetic vulnerability for the disease when using attention vulnerability markers. In this cases the use of abuse drugs probably have had important aetiological implications.