So far, research on the long-term effects of chronic multiple drug abuse regarding specific neurocognitive function deficits has been only tentative. However, also regarding rehabilitation of mostly young long-time addicts, studies are urgently needed (e.g., ability to drive or operate machinery) which are directed at the typical abuse clusters (e.g., alcohol and cannabis) of subgroups in a heterogeneous cohort of drug users.

A group of 750 drug users was examined and the cognitive function deficits in various attentiveness systems compared against the retrospectively detected drug use pattern. Type, extent and stability of drug use were folowed back for 10 years.

The study subjects used drugs of different effects: While morphine was hardly associated with serious cognitive function deficits, with cannabis both the cumulative lifetime dosage and the duration of use correlated with subtle disorders of multimodal stimulus processing and control of eye movement. Cumulative use of alcohol also had a negative effect on the cognitive functions, particularly working memory and the frontal executive functions. The effect of amphetamines, methamphetamines and cocaine varied depending on which other drugs were used. Comorbidity (e.g., schizophrenia) also was important.

These neurocognitive function disorders can lead to impairment of cognitive functions which may be needed professionally. The implications of these results for diagnosis and therapy of comorbid multiple drug users are discussed by means of cases typically seen in rehabilitation centers.