BDNF and major depressive disorder: This review primarily explores the influence of the BDNF Val66Met polymorphism on body weight regulation among patients with a range of psychiatric disorders, including schizophrenia, anorexia nervosa, and bulimia nervosa (eating disorders), bipolar disorder, major depressive disorder, obsessive-compulsive disorder (OCD) and related conditions, post-traumatic stress disorder (PTSD), as well as substance-related and addictive disorders.