Effects of multiple drug abuse on neurocognitive functioning in the domain of attentiveness functioning have not yet been researched systematically. Furthermore, only a few studies deal with the significance of substance-specific abuse clustering and concomitant psychiatric disorders, and the question of how reversible functional impairment is remains unanswered. This study seeks to clarify some of these issues.

A total of 945 multiple drug users (567 male, 378 female) were examined under controlled abstinence for 6 months at the Rehabilitation Center. Neuropsychological tests were done at the time of admission, after four weeks of withdrawal therapy (t1), as well as after three (t2) and six months (t3). In addition to intelligence, subjects were given attentiveness tests (i.e., alertness, divided attention, flexibility, intermodal comparison, incompatibility, working memory, Go/NoGo, visual scanning) using a computerised test battery and compared to normals, pure cannabis users and schizophrenics without drug abuse.

The substance abuse group showed significant decreases in all attentiveness functions (p<0.0001), with patients suffering from concomitant schizophrenic disorders showing greater decreases (p<0.05). These decreases were stable during follow-up. Depending on the specific substance abuse clustering, there were different restitution effects.

These results show the importance of different factors for cognitive long-term effects of multiple drug abuse especially in the domain of attentiveness functions.