Attention-deficit/hyperactivity disorder (ADHD) is a common neurodevelopmental disorder that often persists into adulthood and is accompanied by comorbid mental health problems. This cross-sectional cohort study analyzed 411 18-year-olds from the Danish COPSAC(2000) birth cohort to investigate the relationship between the gut microbiome, fasting and postprandial systemic inflammation, ADHD symptoms, and symptoms of anxiety, stress, and depression. ADHD was assessed using the Adult ADHD…