Substance use and substance use disorders (SUD) are highly (and increasing) prevalent both as single disorders and within the context of complex psychiatric and somatic comorbidities. In parallel with the impact of these disorders, research on addictive processes has significantly expanded in recent decades. However, several challenges remain to be addressed on multiple levels. Within the context of continuing evolution of new (illicit and prescription) drugs of abuse and changes in the growing field of behavioral (nonchemical) addictions (gambling, gaming), the epidemiological situation is rapidly changing. On the level of disorder conceptualization and underlying pathogenetic mechanisms many challenges remain to be addressed, impacting a broad spectrum from legislation and public mental health issues to underlying neurobiological processes such as neuroimmune mechanisms and microbiome, and cognitive dimensions. These provide new targets of therapeutic approaches such as neuromodulation, personalized pharmacotherapy, and contingency management.

In the past few decades, the notion of what constitutes addictive behavior has expanded to include nonsubstance-related behaviors. The World Health Organization recently recognized gambling and gaming disorders as addictive behaviors, and there has been support in the field to include compulsive sexual behaviors as well. Considerable support for reclassification of these behaviors from impulse-control disorders to addictive behaviors has come from studies showing neurobiological similarities with substance use disorders. Behavioral addictions have been found to have similar neurobiological correlates with each other and with substance use disorders on multiple levels of analysis such as alterations in availability of receptors in mesolimbic pathways, the amplitudes of cue-induced late potentials, and frontostriatal activity during reward-based tasks. The implicated neuropathological features support the inclusion of nonsubstance behaviors as addictive behaviors.