IntroductionMental health monitoring is crucial to long-term recovery in substance use disorder (SUD) treatment; however, little is known about how changes in physiological indicators align with changes in self-reported mental health over time.MethodsWe examined longitudinal associations of resting heart rate (RHR) and heart rate variability (HRV) collected via a WHOOP® photoplethysmography device with self-reported stress, anxiety, and depressive symptoms among individuals in SUD treatment. Par