GCG and major depressive disorder: Beyond those reviewed here, there are many further novel promising targets for improving cognitive impairment in MDD where placebo-controlled RCTs have yet to demonstrate cognitive improvement in MDD, or the agents have not yet crossed the preclinical threshold, including creatine, α2-adrenergic receptor antagonists, glucagon-like peptide-1 agonists, GABAB receptor agonists, 5-HT1A biased agonists, and histamine H3 receptor antagonists.