Background: Substance use disorders (SUDs) are chronic relapsing conditions with high relapse rates and substantial burden. Inpatient rehabilitation length of stay (LOS) has been identified internationally as a determinant of treatment outcome, but evidence from Saudi Arabia is limited. This study examined the association between inpatient LOS and relapse, and identified demographic and clinical factors associated with relapse. Methods: A retrospective cross-sectional correlational study using inpatient medical records and follow-up data at ReLib Behavioral Rehabilitation Center, Riyadh. Records of 125 adult patients (aged 18 years or above) admitted between January and December 2025 were reviewed. Patients were observed from discharge to a common census date of 30 June 2026 (median follow-up 306 days, IQR 164–424). Relapse was the primary outcome. Analyses comprised chi-square and Fisher’s exact tests, the Mann–Whitney U test, and multivariable binary logistic regression with collinearity diagnostics. Sensitivity analyses restricted the cohort to patients with guaranteed minimum follow-up... Continue Reading