Mental health conditions and substance use disorders (SUDs) commonly present as co-occurring conditions (Wilson et al., 2018, Hides et al., 2015, Kendler et al., 2019, Lai et al., 2015). When addressed in the clinical setting, mental health problems in people with SUDs are often diagnosed as substance-induced mental disorders (SIMD) (Wilson et al., 2018, Hides et al., 2015, Kendler et al., 2019). Yet, it has been shown, as early as the first wave of the National Epidemiologic Survey on Alcohol and Related Conditions (NESARC), (Hasin and Grant, 2015, Hasin and Kilcoyne, 2012, Grant et al., 1995) that 25–50 % of people seeking treatment for SUDs meet criteria for primary mental disorders (PMD), (Grant et al., 2004, Goldner et al., 2014, McHugh and Weiss, 2019, Jaremko et al., 2015) meaning diagnoses that arise independently from a substance-induced or other medical condition (Grant et al., 2004). Notably, the NESARC estimated that the prevalence of independent SIMD was uncommon (0.1 %) after thoroughly accounting for baseline psychiatric history and clinical observation during sobriety.

Differentiating PMD and SIMD can present a diagnostic dilemma with consequences for both mental health and SUD treatment outcomes. Clinicians often do not have the opportunity to observe people with provisional SIMD during periods of sustained abstinence, a process that is essential for achieving diagnostic clarity. The resulting diagnostic confusion can impact mental health care quality because a common intervention for SIMD is substance use cessation rather than psychopharmacologic intervention to relieve mental health symptoms (Hasin and Grant, 2015, Hasin and Kilcoyne, 2012, Grant et al., 1995). In addition, emphasis on cessation in lieu of psychopharmacotherapy can impact SUD treatment outcomes since mental health symptoms are common triggers for substance use (Krawczyk et al., 2017, Andersson et al., 2019).

Opioid use disorder (OUD) represents a particularly important context for examining SUD treatment outcomes among people who receive SIMD diagnoses. OUD treatment emphasizes evidence-based medications for OUD (MOUD: buprenorphine, methadone, and extended-release naltrexone), which provide substantial reduction in risk for opioid overdose (Sordo et al., 2017, Xu et al., 2022). Yet, use of these medications remains quite low, particularly in certain populations such as those with co-occurring mental health problems. For example, existing literature suggests that people with co-occurring mental health problems are less likely to initiate (Tilhou et al., 2025) and be retained in OUD treatment (Krawczyk et al., 2017, Xu et al., 2023). In particular, depression and stress disorders may increase risk of discontinuation, though findings are highly variable across study, demographic group, and diagnosis (Jaremko et al., 2015, Gelkopf et al., 2006, Butelman et al., 2025, Friesen and Kurdyak, 2020, Ghabrash et al., 2020). Importantly, clinical studies have shown that, despite high documented rates of SIMD, nearly one-third of people with severe OUD exhibit symptoms during periods of abstinence consistent with PMD (Grant et al., 2004, Bramness et al., 2024, Jones and McCance-Katz, 2019, Schuckit, 2006). Rodent studies further suggest the inextricability of substance SIMD and PMD in demonstrating prolonged depressant- and anxiety-like effects even after classic withdrawal has abated (Ozdemir et al., 2023, Welsch et al., 2020). Given the potential for SIMD diagnosis to interfere with treatment for both PMDs and SUDs, analyses describing disparities in MOUD treatment outcomes associated with SIMD verse PMD are needed. To fill this gap, we examined the association of SIMD diagnoses with time to discontinuation of MOUD using a large national administrative insurance claims database in the U.S.