Abstract
Introduction: Polysubstance use is a prevalent substance use pattern with adverse effects on psychological distress and diminished treatment outcomes. Although polysubstance use often dominates clinical practice, the trajectories of substance use and psychological distress in the initial phase of treatment have been subject to few empirical investigations.

Material and Methods: 141 patients initiating inpatient or outpatient treatment for substance use disorder were followed for 12 months, using multiple assessments. We assessed psychological distress and substance use at baseline...