The reality of comorbidity: Depression and drug abuse

Abstract

The comorbidity of drug abuse with depression is well established and has important therapeutic and prognostic implications. Although there is significant understanding of the environmental and neurobiological factors involved in depression and drug addiction considered separately, the mechanisms underlying comorbidity are not well understood. It is likely that the high prevalence of co-occurrence of these two disorders reflects, in part, overlapping environmental, genetic, and neurobiological factors (Figure 1). It is also possible that there will be differences in the neurobiology of comorbidity depending on the temporal course of its development (i.e., depression followed by drug abuse versus drug abuse followed by depression). It is possible that in the former, drugs are used in attempts to self-medicate the depressive state, whereas in the latter it is possible that early exposure to chronic drugs of abuse might lead to neurobiological changes that increase the risk of depression. Areas of overlap in depression and addiction will be discussed here to identify pertinent areas of research for understanding the neurobiology of their comorbidity.