Editorial

“Dual disorders” (DD) is the term used in the mental health field to refer to those who have an addictive disorder and other mental health disorder. They can occur simultaneously but also sequentially; this is an important point to emphasize because, if neglected, it can dramatically expand the number of patients with DD that are misdiagnosed (Szerman et al. Reference Szerman, Torrens, Maldonado, Balhara, Salom, Maremmani, Sher, Didia-Attas, Chen and Baler2022). The two diseases interact so that the addiction problem worsens the other mental health problems and vice versa.

For a long time, our field has been plagued by a lack of clarity about whether addictions are mental disorders – therefore disorders of the brain – or behavioral problems caused by chronic use of a drug that generates neuroplastic changes in the brain leading to addiction. Despite their inclusion in classifications of mental illness, “psychiatric disorders” and “addictive disorders” continue to be discussed as different entities.

For over a century, psychiatric disorders, including substance use disorders, have been defined by expert opinion and clinical observation. The new “Diagnostic and Statistical Manual of Mental Disorders” (DSM) is based on a consensus of experts to define categorical syndromes based on groups of symptoms and signs following the criteria of Kraepelin in 1915 (Hoff, Reference Hoff2015). But as we close this first quarter of the 21st century, it is increasingly important to incorporate advances in neuroscience, considering concepts such as neurodiversity (Johnson & Ahluwalia, Reference Johnson and Ahluwalia2025) and precision psychiatry (Tsikonofilos et al. Reference Tsikonofilos, Kumar, Ampatzis, Garrett and Mansson2025).

It should be noted that the main psychoactive substances, tobacco, alcohol, cannabis, stimulants, and opioids, are chemical substances that affect brain function by interfering with one or more endogenous signaling systems that display a high combined variance among different people. Hence, their effect on mental, emotional, cognitive, and behavioral states will vary depending on individual brain differences. For example, stimulants improve ADHD in people with this mental disorder, but the effect will be different in people without ADHD (Attention-Deficit/Hyperactivity Disorder). These interindividual differences may extend to all psychoactive substances.

Moreover, recent research, originating from the NIH ABCD study (Miller et al. Reference Miller, Baranger, Paul, Garavan, Mackey, Tapert, LeBlanc, Agrawal and Bogdan2024), highlights important neuroanatomical differences between adolescents with greater vulnerability to early substance use and those with lower risk. These differences are based on the structural and functional development of the brain, particularly in regions related to impulse regulation, decision-making, and emotional processing. Here’s how these neurobiological differences contribute to addiction risk and other mental health disorders: The findings highlight the existence of pre-existing brain variability and vulnerability that predisposes to subbstance use disorders (SUD) and other mental disorders, challenging the dominant proposition that these mental disorders, including addiction, are mainly a consequence of substance use. These differences in dysfunctional brain circuits and systems will give rise to different manifestations of mental disorders and not only to the compulsive use of certain substances. Disorders that share genetic, neurobiological, and environmental (e.g., epigenetic) etiological factors are likely to co-occur.

Neuroscience has shown that addictive and other mental disorders often display sets of interconnected and/or overlapping brain processes, rather than being disorders primarily defined by a single behavior (such as uncontrollable excessive drug use) (Volkow et al. Reference Volkow, Torrens, Poznyak, Saenz, Busse, Kashino, Krupchanka, Kestel, Campello and Gerra2020). This clinical condition of DDs is not recognized by standard diagnostic instruments intended to categorize and classify mental disorders, which place an overemphasis on substance-induced mental disorders.

The competition between the different philosophies, schools of thought, and their many (often contradictory) terms used to describe these highly prevalent clinical conditions hinders progress and is made evident by the lack of consensus on how to name this clinical condition:

• The World Health Organization (WHO) often speaks of “dual diagnosis” when an SUD occurs simultaneously with another psychiatric disorder in the same person. However, the DSM indicates that the diagnosis should be made even if the addiction is in remission. This term also does not include a clinical connection between both symptomatic manifestations nor that it also encompasses two or more SUDs or other psychiatric disorders (WHO, 1994). This may help explain why this organization has begun to use the term DD, at least in one of its more recent reports (Volkow et al. Reference Volkow, Torrens, Poznyak, Saenz, Busse, Kashino, Krupchanka, Kestel, Campello and Gerra2020).

• Meanwhile, the European Monitoring Centre for Drugs and Drug Addiction (EMCDDA), now renamed as European Union Drugs Agency (EUDA), has used the terms “comorbidity” (EMCDDA, 2016) and “dual diagnosis” (Torrens et al. Reference Torrens, Mestre-Pinto, Montanari, Vicente and Domingo-Salvany2017) interchangeably to describe the “temporal” coexistence of two or more psychiatric disorders, without mentioning that SUDs are also mental disorders, as they are defined by the International Classification of Diseases (ICD), when one of them is problematic substance use (WHO, 2019).

• The American Association of Addiction Medicine (ASAM)’s criteria for patient placement also uses dual diagnosis, although interchangeably with yet another term “co-occurring disorder” (COD) (Stallvik & Nordahl, Reference Stallvik and Nordahl2014).

• The US Substance Abuse and Mental Health Services Administration (SAMHSA) also uses the term co-occurring disorder (SAMHSA, 2021).

• Meanwhile, in the Spanish, French, Portuguese, and Italian languages, the most widespread and accepted term is “dual pathology” (Szerman et al. Reference Szerman, Martinez-Raga, Peris, Roncero, Basurte, Vega, Ruiz and Casas2013).

• In Norway and some other Nordic countries, the term dual diagnosis has been abandoned as these patients might have many co-occurring somatic disorders. The entity used is therefore patients with addiction and mental disorders.

As for the different alternative terms we have mentioned, it is interesting to remember that the term “comorbidity” was coined by Feinstein in the 1970s to identify two medical conditions that coexist in time but are not related to each other (Feinstein, Reference Feinstein1970). Co-occurring disorders and dual diagnosis are based on the same concept. This debate goes back many years, when it was proposed that the definition of comorbidity simply specifies an association in time, not necessarily a causal relationship, between conditions (Kaplan et al. Reference Kaplan, Crawford, Cantell, Kooistra and Dewey2006). This state of affairs unnecessarily exacerbates the inherent challenge stemming from the complexity of the underlying conditions (Szerman et al. Reference Szerman, Torrens, Maldonado, Balhara, Salom, Maremmani, Sher, Didia-Attas, Chen and Baler2022). The lack of a standardized term adds confusion, fuels stigma, and contributes not only to discrimination but also to the so-called “wrong-door syndrome” (Szerman et al. Reference Szerman, Torrens, Maldonado, Balhara, Salom, Maremmani, Sher, Didia-Attas, Chen and Baler2022) that captures the difficulty of not only diagnosing but also treating addictions and other mental disorders in an integrated (one-stop-shop) fashion. Confusion, discrimination, and stigma make up a perfect cocktail to drive people away from seeking the care they need, likely exacerbating their complex condition (Szerman et al. Reference Szerman, Torrens, Maldonado, Balhara, Salom, Maremmani, Sher, Didia-Attas, Chen and Baler2022).

The World Association on Dual Disorders (WADD) proposes the adoption of the term “dual disorders” when referring to patients who have an addictive disorder and other mental disorders (either simultaneously or sequentially). While this proposal is still arbitrary, it would help harmonize various clinical and research efforts by rallying around a single, more accurate, and less stigmatizing designation.

Adopting a nomenclature based on dual disorder could increase clinicians’ awareness of the intimate and transdiagnostic relationships between signs and symptoms of addictive disorders and other mental disorders. This will help them address their etiologies and clinical manifestations in a more integrated, personalized (precision psychiatry), and effective manner (Volkow et al. Reference Volkow, Torrens, Poznyak, Saenz, Busse, Kashino, Krupchanka, Kestel, Campello and Gerra2020).