This chapter examines the relationship between eating disorders, specifically anorexia nervosa and bulimia nervosa, and substance use during adolescence, based on the criteria defined in the DSM-5-TR. Anorexia nervosa is characterized by a persistent restriction of energy intake, leading to significantly low body weight, with a complex etiology involving biological, psychological, social, and cultural factors. The neurobiological basis of the disorder includes impairments in executive functions, alterations in reward processing, and deficits in social cognition, with evidence of psychiatric comorbidities and substance use, particularly in the binge-eating/purging subtype. Studies demonstrate a significant prevalence of substance use among adolescents with anorexia, often associated with compensatory behaviors, such as “drunkorexia”, where individuals restrict calories to compensate for alcohol consumption. Meanwhile, bulimia nervosa involves recurrent episodes of binge eating followed by compensatory behaviors, with a strong influence of body shape on self-evaluation. The neurobiological bases of bulimia include alterations in serotonin and dopamine systems, cognitive deficits, and impulse control problems. Adolescents with bulimia show higher rates of substance use, including alcohol, tobacco, and other drugs, often as coping mechanisms for the emotional and psychological challenges of the disorder. Given the high rate of comorbidity and health risks, this chapter emphasizes the need for integrated and multidisciplinary approaches to the diagnosis and treatment of these disorders, addressing both eating behaviors and substance use.