Early Substance Use Trajectory as a Marker of Clinical Severity Among Treatment-Seeking Patients with Substance Use Disorders in Iran

Abstract

Background: Age at first substance use is an established developmental marker; however, age at initiation alone may not capture how rapidly substance use progresses. Objectives: This study examined age at first use, transition time to daily use, and age at daily use in relation to clinical severity among treatment-seeking patients with substance use disorders in Iran. Methods: This analytical cross-sectional study used baseline data from 170 adults recruited by convenience sampling from selected outpatient addiction treatment clinics in Tehran. The primary trajectory indicators were age at first substance use, age at onset of daily substance use, and the interval between these events. Early onset of daily use (≤ 22 years) was used as a secondary categorical indicator corresponding to the first quartile of the sample distribution. Outcomes included dependence severity (Leeds Dependence Questionnaire [LDQ], Substance Dependence Severity Scale [SDSS]), general health (28-item General Health Questionnaire [GHQ-28]), cigarette consumption, dose-escalation steps, treatment history, and social and behavioral indicators. Multivariable linear models were fitted using HC3 heteroskedasticity-robust standard errors. Results: The mean age at first use was 20.60 ± 3.75 years, and the mean age at initiation of daily use was 25.21 ± 4.42 years. In robust adjusted models, a shorter transition time was associated with higher LDQ (B = -0.316, P = 0.006), higher SDSS (B = -0.332, P = 0.001), and greater dose escalation (B = -0.153, P < 0.001). An earlier age at initiation of daily use was independently associated with higher LDQ and SDSS scores, heavier cigarette smoking, greater dose escalation, and more previous residential/camp admissions. Conclusions: An earlier transition to daily substance use, particularly a younger age at initiation of daily use, was associated with a more severe clinical profile and greater social vulnerability. These history-based indicators may complement routine assessment and risk stratification.