Primary vs. secondary diagnosis is a thing of the past.
California’s Department of Healthcare Services (DHCS) has been moving away in recent years from the siloed and separate treatment of mental health and substance use disorders. Overall, nationally, in the behavioral healthcare world, the effort to determine a “primary” diagnosis vs. a “secondary” diagnosis has been de-emphasized and has largely gone away. For example, the DSM-5 no longer uses the phrase “primary diagnosis.” now, “disorders are listed together … without formal differentiation” (APA, 2022, p. 15). There’s a reason for this, and this is particularly relevant in the area of integrated substance use and mental health treatment. Significant research suggested that bidirectional causality is typical. In other words, the research found, mental health symptoms predicted later substance use and substance use predicted later mental health symptoms (Kessler et al., 2005). A recent study found similar evidence for bidirectional association: cannabis-related problems predicted later increases in depressive symptoms and depressive symptoms also predicted later cannabis-related consequences (Halliday, J. et al., 2025). Although California’s DHCS has been moving away from siloed treatment, as suggested by their “No Wrong Door” policy initiative, the distinct mental health and SUD programs and separate Medi-Cal funding streams still persist. I’d like to encourage DHCS to continue to emphasize the need for integrated behavioral healthcare. And even beyond this discussion of integrated mental health and SUD treatment is the equally important dimension of “case management” which often gets segregated into an additional siloed treatment space. Helping to provide linkages to resources for housing, education, vocational pathways, medical care, and so on— could be said to be equally essential and important for people in recovery.
American Psychiatric Association. (2022). Diagnostic and statistical manual of mental disorders (5th ed., text rev.)
Halladay J, Belisario K, McDonald A, et al. (2025). Examining bidirectional associations between cannabis use and internalizing symptoms among high-risk emerging adults: A prospective cohort study. Psychological Medicine. 2025;55:e291.
Kessler, R. C., Berglund, P., Demler, O., Jin, R., Merikangas, K. R., & Walters, E. E. (2005). Lifetime prevalence and age-of-onset distributions of DSM-IV disorders in the National Comorbidity Survey Replication. Archives of General Psychiatry, 62(6), 593–602.
