Compared with placebo, low certainty evidence supported the use of five interventions to prevent postoperative delirium: dexmedetomidine with melatonin (RR 0.31, 95%CrI 0.13–0.69, low certainty of evidence); ketamine (RR 0.44, 95%CrI 0.18–0.98, very low certainty of evidence); risperidone (RR 0.34, 95%CrI 0.11–0.89, low certainty of evidence); insulin (RR 0.49, 95%CrI 0.24–0.96, low certainty of evidence); and dexmedetomidine (RR 0.66, 95%CrI 0.50–0.85, low certainty of evidence) (Fig. 2b). This evidence concerns the gene INS and delirium.