Objective: This study aimed to identify factors influencing the length of hospital stay of individuals with substance use disorder (SUD).

Methods: This is a cohort study of patients with SUD admitted to a specialized addiction unit of a large university hospital from February 2015 to September 2019. Generalized Estimating Equations were used to analyze the length of stay. The length of stay (LOS) per episode was regressed on sex, number of hospitalizations, age, Brief Symptom Check List and Health of Nation Outcome Scales (HoNOS) score on admission.

Results: The study included 547 patients with SUD who had 970 admissions during the reported period. Number of hospitalizations and HoNOS scores significantly correlated with LOS per episode. As time passed or equivalently as the number of hospitalizations increased, the LOS per episode tended to decrease while an increased HoNOS score on admission was a significant risk factor of increased LOS. The other predictors were not statistically significant.

Conclusions: Higher HoNOS scores on admission, implying higher overall symptom level and more psychosocial problems were positively associated with increased LOS. In view of these findings, strategies to reduce LOS should focus on improving transition into outpatient treatment, as well as offering sufficient help for psychosocial problems.