INTRODUCTION: Alcohol use among patients in treatment for illicit substance use disorder (SUD) is often overlooked, at best perceived as a secondary issue, despite growing evidence of exacerbated negative health outcomes among polysubstance users. METHOD: We analyse a nationwide dataset on patients entering treatment for cannabis, opioid, and stimulant use disorders in France between 2012 and 2022. We conduct multilevel logistic regressions to determine the main predictors of problematic alcohol use (PAU) among patients who entered treatment for cannabis (n = 308,906), opioid (n = 255,879) or stimulant (n = 60,211) use disorders. RESULTS: PAU remains a common behaviour among patients with SUD (overall prevalence: 28.2%, 95% confidence interval [CI] 28.1-28.3), with lower prevalence among patients treated for cannabis (27.3%, 95% CI 27.2-27.5) and opioid disorders (27.2%, 95% CI 27.0-27.4), and higher for patients treated for stimulant disorders (36.8%, 95% CI 36.4-37.2). There is an increase in PAU over time for each of the SUD leading to treatment (23.0% in 2012 vs. 29.5% in 2022
23.3% vs. 31.4% and 29.7% vs. 38.9% respectively). Males, older people, early onset, current use of tobacco, and psychiatric comorbidities are positively associated with PAU. DISCUSSION AND CONCLUSIONS: The increasing prevalence of problematic alcohol use among patients treated for SUD in France remains a source of concern. Screening for both alcohol and drug use among patients in treatment presents a crucial opportunity to prevent and treat SUDs early, especially among patients treated for stimulants.