Substance use disorder (SUD) is a major global public health challenge, frequently co-occurring with psychiatric conditions such as attention-deficit/hyperactivity disorder (ADHD). Endocannabinoid system (ECS) dysregulation has been implicated in both SUD and ADHD, but the interplay between these conditions remains poorly understood. This study investigates plasma concentrations of endocannabinoid-congeners in individuals with SUD, with and without comorbid ADHD, to identify potential…