Cannabinoid Receptor (CB1) Agonist Treatment in Severe Chronic Anorexia Nervosa

Inclusion Criteria: * Patients under treatment for AN. * Patients attending ambulatory treatment, which are not expected to be admitted at the hospital with AN-related pathology or discharged during the study period. * Patients admitted to Department of Endocrinology M or Psychiatric Department P which are not expected to be discharged during the study period. * Age over 18. * Duration of the disease over 5 years. Exclusion Criteria: * Patients under compulsory treatment or suffering of mania, schizophrenia or primary depression. * Patients with any medical or psychiatric event related or not related to the underlying eating disorder which requires prolonged admission to the hospital during the study. * Patients with unstable heart disease (relevant changes in medication prior or during the study) and limitation of activity (not comfortable with more than moderate exertion / at rest). * Patients not attending to the weekly controls. * If other severe adverse events (SAE) / drug reactions (SADR) are suspected. * Patients actually having or having a history of alcohol, cannabis, opioids or central stimulating drugs abuse. * Patients with known allergy to dronabinol or sesame oil. * Fertile, menstruating women not using safe contraception. * Pregnancy.