Brain-derived neurotrophic factor (BDNF) is found throughout the brain and is involved in neurogenesis and neuroplasticity, having a potential role in the pathophysiology of many neuropsychiatric disorders.5 Several studies have assessed BDNF levels in various neuropsychiatric disorders (that is, major depression,6, 7 bipolar disorder8 and schizophrenia9, 10), and evidence suggests that BDNF levels are significantly decreased in these disorders. Here, BDNF is linked to major depressive disorder.