Altered cortisol regulation is implicated in Attention-Deficit/Hyperactivity Disorder (ADHD), but causality remains debated. While meta-analyses suggest that lower basal cortisol levels, especially in the morning, correlate with ADHD, study heterogeneity prompts further inquiry. Leveraging post-genome-wide association approaches, we examined morning cortisol levels (n = 25,314) and ADHD (n = 225,543). We employed seven Mendelian Randomization methods for causal inference, assessed global and…
