Furthermore, research already implicates BDNF (Guyon et al 2021) and NMDA receptors (Zhang et al 2021) in aggression and BDNF, nitric oxide and kynurenine are all linked to ADHD (Molina-Carballo et al. 2021; Sharma et al. 2021; Sari et al. 2020), suggesting these mechanisms may be particularly relevant to the studies reviewed here. Here, BDNF is linked to attention deficit-hyperactivity disorder.