Additionally, neurotrophic factors such as brain-derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF), insulin-like growth factor-1 (IGF-1), and vascular endothelial growth factor (VEGF) have been investigated as potential biomarkers in psychiatric disorders, including SUDs21–24. This evidence concerns the gene IGF1 and psychiatric disorder.