Nevertheless, some physiological or pathological conditions have been associated with a reduction in the abundance of ABCB1 and ABCG2 at the BBB as for instance healthy ageing or Alzheimer’s disease (Kannan et al., 2017; Storelli et al., 2020), which may raise the risk for ABCB1-mediated DDIs at the BBB and central side effects in the elderly (Bauer et al., 2017; Bauer et al., 2021). This evidence concerns the gene ABCG2 and Alzheimer disease.