NEFL and attention deficit-hyperactivity disorder: Plasma NfL‐levels were not significantly different between participants with ADHD (median = 10.80 pg/ml, SD = 6.22 pg/mL) and controls (median = 7.58 pg/mL, SD = 6.41pg/mL), as tested by two‐sample Mann–Whitney U (U = 387, P = 0.139, effect size Z = 0.19).